diff --git a/mmtk/Cargo.lock b/mmtk/Cargo.lock
index 7723a44..6c8d602 100644
--- a/mmtk/Cargo.lock
+++ b/mmtk/Cargo.lock
@@ -13,9 +13,9 @@ dependencies = [
 
 [[package]]
 name = "anstream"
-version = "0.6.19"
+version = "0.6.20"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "301af1932e46185686725e0fad2f8f2aa7da69dd70bf6ecc44d6b703844a3933"
+checksum = "3ae563653d1938f79b1ab1b5e668c87c76a9930414574a6583a7b7e11a8e6192"
 dependencies = [
  "anstyle",
  "anstyle-parse",
@@ -43,22 +43,22 @@ dependencies = [
 
 [[package]]
 name = "anstyle-query"
-version = "1.1.3"
+version = "1.1.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6c8bdeb6047d8983be085bab0ba1472e6dc604e7041dbf6fcd5e71523014fae9"
+checksum = "9e231f6134f61b71076a3eab506c379d4f36122f2af15a9ff04415ea4c3339e2"
 dependencies = [
- "windows-sys",
+ "windows-sys 0.60.2",
 ]
 
 [[package]]
 name = "anstyle-wincon"
-version = "3.0.9"
+version = "3.0.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "403f75924867bb1033c59fbf0797484329750cfbe3c4325cd33127941fabc882"
+checksum = "3e0633414522a32ffaac8ac6cc8f748e090c5717661fddeea04219e2344f5f2a"
 dependencies = [
  "anstyle",
  "once_cell_polyfill",
- "windows-sys",
+ "windows-sys 0.60.2",
 ]
 
 [[package]]
@@ -94,9 +94,9 @@ checksum = "c08606f8c3cbf4ce6ec8e28fb0014a2c086708fe954eaa885384a6165172e7e8"
 
 [[package]]
 name = "bitflags"
-version = "2.9.1"
+version = "2.9.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1b8e56985ec62d17e9c1001dc89c88ecd7dc08e47eba5ec7c29c7b5eeecde967"
+checksum = "34efbcccd345379ca2868b2b2c9d3782e9cc58ba87bc7d79d5b53d9c9ae6f25d"
 
 [[package]]
 name = "built"
@@ -124,14 +124,14 @@ checksum = "3fa76293b4f7bb636ab88fd78228235b5248b4d05cc589aed610f954af5d7c7a"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.104",
+ "syn 2.0.106",
 ]
 
 [[package]]
 name = "cc"
-version = "1.2.30"
+version = "1.2.34"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "deec109607ca693028562ed836a5f1c4b8bd77755c4e132fc5ce11b0b6211ae7"
+checksum = "42bc4aea80032b7bf409b0bc7ccad88853858911b7713a8062fdc0623867bedc"
 dependencies = [
  "jobserver",
  "libc",
@@ -140,9 +140,9 @@ dependencies = [
 
 [[package]]
 name = "cfg-if"
-version = "1.0.1"
+version = "1.0.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9555578bc9e57714c812a1f84e4fc5b4d21fcb063490c624de019f7464c91268"
+checksum = "2fd1289c04a9ea8cb22300a459a72a385d7c73d3259e2ed7dcb2af674838cfa9"
 
 [[package]]
 name = "colorchoice"
@@ -220,7 +220,7 @@ checksum = "6178a82cf56c836a3ba61a7935cdb1c49bfaa6fa4327cd5bf554a503087de26b"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.104",
+ "syn 2.0.106",
 ]
 
 [[package]]
@@ -252,7 +252,7 @@ checksum = "f282cfdfe92516eb26c2af8589c274c7c17681f5ecc03c18255fe741c6aa64eb"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.104",
+ "syn 2.0.106",
 ]
 
 [[package]]
@@ -280,9 +280,9 @@ dependencies = [
 
 [[package]]
 name = "form_urlencoded"
-version = "1.2.1"
+version = "1.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e13624c2627564efccf4934284bdd98cbaa14e79b0b5a141218e507b3a823456"
+checksum = "cb4cb245038516f5f85277875cdaa4f7d2c9a0fa0468de06ed190163b1581fcf"
 dependencies = [
  "percent-encoding",
 ]
@@ -326,9 +326,9 @@ checksum = "fc0fef456e4baa96da950455cd02c081ca953b141298e41db3fc7e36b1da849c"
 
 [[package]]
 name = "idna"
-version = "1.0.3"
+version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "686f825264d630750a544639377bae737628043f20d38bbc029e8f29ea968a7e"
+checksum = "3b0875f23caa03898994f6ddc501886a45c7d3d62d04d2d90788d47be1b1e4de"
 dependencies = [
  "idna_adapter",
  "smallvec",
@@ -363,7 +363,7 @@ checksum = "e04d7f318608d35d4b61ddd75cbdaee86b023ebe2bd5a66ee0915f0bf93095a9"
 dependencies = [
  "hermit-abi",
  "libc",
- "windows-sys",
+ "windows-sys 0.59.0",
 ]
 
 [[package]]
@@ -402,14 +402,14 @@ checksum = "03343451ff899767262ec32146f6d559dd759fdadf42ff0e227c7c48f72594b4"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.104",
+ "syn 2.0.106",
 ]
 
 [[package]]
 name = "jobserver"
-version = "0.1.33"
+version = "0.1.34"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "38f262f097c174adebe41eb73d66ae9c06b2844fb0da69969647bbddd9b0538a"
+checksum = "9afb3de4395d6b3e67a780b6de64b51c978ecf11cb9a462c66be7d4ca9039d33"
 dependencies = [
  "getrandom",
  "libc",
@@ -423,9 +423,9 @@ checksum = "bbd2bcb4c963f2ddae06a2efc7e9f3591312473c50c6685e1f298068316e66fe"
 
 [[package]]
 name = "libc"
-version = "0.2.174"
+version = "0.2.175"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1171693293099992e19cddea4e8b849964e9846f4acee11b3948bcc337be8776"
+checksum = "6a82ae493e598baaea5209805c49bbf2ea7de956d50d7da0da1164f9c6d28543"
 
 [[package]]
 name = "libgit2-sys"
@@ -485,7 +485,7 @@ dependencies = [
 [[package]]
 name = "mmtk"
 version = "0.31.0"
-source = "git+https://github.com/mmtk/mmtk-core.git?rev=31a78a41f02fc7228780b501c4944ba750e32ee4#31a78a41f02fc7228780b501c4944ba750e32ee4"
+source = "git+https://github.com/mmtk/mmtk-core.git?rev=6eb1328bfce34a7e0fc4b84fd0b65a849b083e0e#6eb1328bfce34a7e0fc4b84fd0b65a849b083e0e"
 dependencies = [
  "atomic",
  "atomic-traits",
@@ -511,6 +511,7 @@ dependencies = [
  "num_cpus",
  "portable-atomic",
  "probe",
+ "rayon-core",
  "regex",
  "rustversion",
  "spin",
@@ -523,12 +524,12 @@ dependencies = [
 [[package]]
 name = "mmtk-macros"
 version = "0.31.0"
-source = "git+https://github.com/mmtk/mmtk-core.git?rev=31a78a41f02fc7228780b501c4944ba750e32ee4#31a78a41f02fc7228780b501c4944ba750e32ee4"
+source = "git+https://github.com/mmtk/mmtk-core.git?rev=6eb1328bfce34a7e0fc4b84fd0b65a849b083e0e#6eb1328bfce34a7e0fc4b84fd0b65a849b083e0e"
 dependencies = [
  "proc-macro-error",
  "proc-macro2",
  "quote",
- "syn 2.0.104",
+ "syn 2.0.106",
 ]
 
 [[package]]
@@ -587,9 +588,9 @@ checksum = "a4895175b425cb1f87721b59f0f286c2092bd4af812243672510e1ac53e2e0ad"
 
 [[package]]
 name = "percent-encoding"
-version = "2.3.1"
+version = "2.3.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e3148f5046208a5d56bcfc03053e3ca6334e51da8dfb19b6cdc8b306fae3283e"
+checksum = "9b4f627cb1b25917193a259e49bdad08f671f8d9708acfd5fe0a8c1455d87220"
 
 [[package]]
 name = "pkg-config"
@@ -644,9 +645,9 @@ dependencies = [
 
 [[package]]
 name = "proc-macro2"
-version = "1.0.95"
+version = "1.0.101"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "02b3e5e68a3a1a02aad3ec490a98007cbc13c37cbe84a3cd7b8e406d76e7f778"
+checksum = "89ae43fd86e4158d6db51ad8e2b80f313af9cc74f5c0e03ccb87de09998732de"
 dependencies = [
  "unicode-ident",
 ]
@@ -688,9 +689,9 @@ dependencies = [
 
 [[package]]
 name = "regex"
-version = "1.11.1"
+version = "1.11.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b544ef1b4eac5dc2db33ea63606ae9ffcfac26c1416a2806ae0bf5f56b201191"
+checksum = "23d7fd106d8c02486a8d64e778353d1cffe08ce79ac2e82f540c86d0facf6912"
 dependencies = [
  "aho-corasick",
  "memchr",
@@ -700,9 +701,9 @@ dependencies = [
 
 [[package]]
 name = "regex-automata"
-version = "0.4.9"
+version = "0.4.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "809e8dc61f6de73b46c85f4c96486310fe304c434cfa43669d7b40f711150908"
+checksum = "6b9458fa0bfeeac22b5ca447c63aaf45f28439a709ccd244698632f9aa6394d6"
 dependencies = [
  "aho-corasick",
  "memchr",
@@ -711,9 +712,9 @@ dependencies = [
 
 [[package]]
 name = "regex-syntax"
-version = "0.8.5"
+version = "0.8.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2b15c43186be67a4fd63bee50d0303afffcef381492ebe2c5d87f324e1b8815c"
+checksum = "caf4aa5b0f434c91fe5c7f1ecb6a5ece2130b02ad2a590589dda5146df959001"
 
 [[package]]
 name = "rustc_version"
@@ -726,9 +727,9 @@ dependencies = [
 
 [[package]]
 name = "rustversion"
-version = "1.0.21"
+version = "1.0.22"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8a0d197bd2c9dc6e53b84da9556a69ba4cdfab8619eb41a8bd1cc2027a0f6b1d"
+checksum = "b39cdef0fa800fc44525c84ccb54a029961a8215f9619753635a9c0d2538d46d"
 
 [[package]]
 name = "scopeguard"
@@ -759,7 +760,7 @@ checksum = "5b0276cf7f2c73365f7157c8123c21cd9a50fbbd844757af28ca1f5925fc2a00"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.104",
+ "syn 2.0.106",
 ]
 
 [[package]]
@@ -791,21 +792,20 @@ checksum = "a2eb9349b6444b326872e140eb1cf5e7c522154d69e7a0ffb0fb81c06b37543f"
 
 [[package]]
 name = "strum"
-version = "0.27.1"
+version = "0.27.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f64def088c51c9510a8579e3c5d67c65349dcf755e5479ad3d010aa6454e2c32"
+checksum = "af23d6f6c1a224baef9d3f61e287d2761385a5b88fdab4eb4c6f11aeb54c4bcf"
 
 [[package]]
 name = "strum_macros"
-version = "0.27.1"
+version = "0.27.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c77a8c5abcaf0f9ce05d62342b7d298c346515365c36b673df4ebe3ced01fde8"
+checksum = "7695ce3845ea4b33927c055a39dc438a45b059f7c1b3d91d38d10355fb8cbca7"
 dependencies = [
  "heck",
  "proc-macro2",
  "quote",
- "rustversion",
- "syn 2.0.104",
+ "syn 2.0.106",
 ]
 
 [[package]]
@@ -820,9 +820,9 @@ dependencies = [
 
 [[package]]
 name = "syn"
-version = "2.0.104"
+version = "2.0.106"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "17b6f705963418cdb9927482fa304bc562ece2fdd4f616084c50b7023b435a40"
+checksum = "ede7c438028d4436d71104916910f5bb611972c5cfd7f89b8300a8186e6fada6"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -845,9 +845,9 @@ dependencies = [
 
 [[package]]
 name = "tinyvec"
-version = "1.9.0"
+version = "1.10.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "09b3661f17e86524eccd4371ab0429194e0d7c008abb45f7a7495b1719463c71"
+checksum = "bfa5fdc3bce6191a1dbc8c02d5c8bffcf557bafa17c124c5264a458f1b0613fa"
 dependencies = [
  "tinyvec_macros",
 ]
@@ -887,13 +887,14 @@ dependencies = [
 
 [[package]]
 name = "url"
-version = "2.5.4"
+version = "2.5.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "32f8b686cadd1473f4bd0117a5d28d36b1ade384ea9b5069a1c40aefed7fda60"
+checksum = "08bc136a29a3d1758e07a9cca267be308aeebf5cfd5a10f3f67ab2097683ef5b"
 dependencies = [
  "form_urlencoded",
  "idna",
  "percent-encoding",
+ "serde",
 ]
 
 [[package]]
@@ -958,7 +959,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "12342cb4d8e3b046f3d80effd474a7a02447231330ef77d71daa6fbc40681143"
 dependencies = [
  "windows-core",
- "windows-targets",
+ "windows-targets 0.52.6",
 ]
 
 [[package]]
@@ -970,7 +971,7 @@ dependencies = [
  "windows-implement",
  "windows-interface",
  "windows-result",
- "windows-targets",
+ "windows-targets 0.52.6",
 ]
 
 [[package]]
@@ -981,7 +982,7 @@ checksum = "9107ddc059d5b6fbfbffdfa7a7fe3e22a226def0b2608f72e9d552763d3e1ad7"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.104",
+ "syn 2.0.106",
 ]
 
 [[package]]
@@ -992,16 +993,22 @@ checksum = "29bee4b38ea3cde66011baa44dba677c432a78593e202392d1e9070cf2a7fca7"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.104",
+ "syn 2.0.106",
 ]
 
+[[package]]
+name = "windows-link"
+version = "0.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5e6ad25900d524eaabdbbb96d20b4311e1e7ae1699af4fb28c17ae66c80d798a"
+
 [[package]]
 name = "windows-result"
 version = "0.1.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "5e383302e8ec8515204254685643de10811af0ed97ea37210dc26fb0032647f8"
 dependencies = [
- "windows-targets",
+ "windows-targets 0.52.6",
 ]
 
 [[package]]
@@ -1010,7 +1017,16 @@ version = "0.59.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1e38bc4d79ed67fd075bcc251a1c39b32a1776bbe92e5bef1f0bf1f8c531853b"
 dependencies = [
- "windows-targets",
+ "windows-targets 0.52.6",
+]
+
+[[package]]
+name = "windows-sys"
+version = "0.60.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f2f500e4d28234f72040990ec9d39e3a6b950f9f22d3dba18416c35882612bcb"
+dependencies = [
+ "windows-targets 0.53.3",
 ]
 
 [[package]]
@@ -1019,14 +1035,31 @@ version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9b724f72796e036ab90c1021d4780d4d3d648aca59e491e6b98e725b84e99973"
 dependencies = [
- "windows_aarch64_gnullvm",
- "windows_aarch64_msvc",
- "windows_i686_gnu",
- "windows_i686_gnullvm",
- "windows_i686_msvc",
- "windows_x86_64_gnu",
- "windows_x86_64_gnullvm",
- "windows_x86_64_msvc",
+ "windows_aarch64_gnullvm 0.52.6",
+ "windows_aarch64_msvc 0.52.6",
+ "windows_i686_gnu 0.52.6",
+ "windows_i686_gnullvm 0.52.6",
+ "windows_i686_msvc 0.52.6",
+ "windows_x86_64_gnu 0.52.6",
+ "windows_x86_64_gnullvm 0.52.6",
+ "windows_x86_64_msvc 0.52.6",
+]
+
+[[package]]
+name = "windows-targets"
+version = "0.53.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d5fe6031c4041849d7c496a8ded650796e7b6ecc19df1a431c1a363342e5dc91"
+dependencies = [
+ "windows-link",
+ "windows_aarch64_gnullvm 0.53.0",
+ "windows_aarch64_msvc 0.53.0",
+ "windows_i686_gnu 0.53.0",
+ "windows_i686_gnullvm 0.53.0",
+ "windows_i686_msvc 0.53.0",
+ "windows_x86_64_gnu 0.53.0",
+ "windows_x86_64_gnullvm 0.53.0",
+ "windows_x86_64_msvc 0.53.0",
 ]
 
 [[package]]
@@ -1035,48 +1068,96 @@ version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "32a4622180e7a0ec044bb555404c800bc9fd9ec262ec147edd5989ccd0c02cd3"
 
+[[package]]
+name = "windows_aarch64_gnullvm"
+version = "0.53.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "86b8d5f90ddd19cb4a147a5fa63ca848db3df085e25fee3cc10b39b6eebae764"
+
 [[package]]
 name = "windows_aarch64_msvc"
 version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "09ec2a7bb152e2252b53fa7803150007879548bc709c039df7627cabbd05d469"
 
+[[package]]
+name = "windows_aarch64_msvc"
+version = "0.53.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c7651a1f62a11b8cbd5e0d42526e55f2c99886c77e007179efff86c2b137e66c"
+
 [[package]]
 name = "windows_i686_gnu"
 version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8e9b5ad5ab802e97eb8e295ac6720e509ee4c243f69d781394014ebfe8bbfa0b"
 
+[[package]]
+name = "windows_i686_gnu"
+version = "0.53.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c1dc67659d35f387f5f6c479dc4e28f1d4bb90ddd1a5d3da2e5d97b42d6272c3"
+
 [[package]]
 name = "windows_i686_gnullvm"
 version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0eee52d38c090b3caa76c563b86c3a4bd71ef1a819287c19d586d7334ae8ed66"
 
+[[package]]
+name = "windows_i686_gnullvm"
+version = "0.53.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9ce6ccbdedbf6d6354471319e781c0dfef054c81fbc7cf83f338a4296c0cae11"
+
 [[package]]
 name = "windows_i686_msvc"
 version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "240948bc05c5e7c6dabba28bf89d89ffce3e303022809e73deaefe4f6ec56c66"
 
+[[package]]
+name = "windows_i686_msvc"
+version = "0.53.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "581fee95406bb13382d2f65cd4a908ca7b1e4c2f1917f143ba16efe98a589b5d"
+
 [[package]]
 name = "windows_x86_64_gnu"
 version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "147a5c80aabfbf0c7d901cb5895d1de30ef2907eb21fbbab29ca94c5b08b1a78"
 
+[[package]]
+name = "windows_x86_64_gnu"
+version = "0.53.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2e55b5ac9ea33f2fc1716d1742db15574fd6fc8dadc51caab1c16a3d3b4190ba"
+
 [[package]]
 name = "windows_x86_64_gnullvm"
 version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "24d5b23dc417412679681396f2b49f3de8c1473deb516bd34410872eff51ed0d"
 
+[[package]]
+name = "windows_x86_64_gnullvm"
+version = "0.53.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0a6e035dd0599267ce1ee132e51c27dd29437f63325753051e71dd9e42406c57"
+
 [[package]]
 name = "windows_x86_64_msvc"
 version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "589f6da84c646204747d1270a2a5661ea66ed1cced2631d546fdfb155959f9ec"
 
+[[package]]
+name = "windows_x86_64_msvc"
+version = "0.53.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "271414315aff87387382ec3d271b52d7ae78726f5d44ac98b4f4030c91880486"
+
 [[package]]
 name = "wit-bindgen-rt"
 version = "0.39.0"
diff --git a/mmtk/Cargo.toml b/mmtk/Cargo.toml
index ce087c8..1b2940b 100644
--- a/mmtk/Cargo.toml
+++ b/mmtk/Cargo.toml
@@ -12,7 +12,7 @@ edition = "2021"
 # Metadata for the Ruby repository
 [package.metadata.ci-repos.ruby]
 repo = "mmtk/ruby" # This is used by actions/checkout, so the format is "owner/repo", not URL.
-rev = "64c07dcd7ca763e25607848df3be909135e02589"
+rev = "fe51e6277b4df810a90c4474f951ed0a263acea0"
 
 [lib]
 name = "mmtk_ruby"
@@ -37,7 +37,7 @@ features = ["is_mmtk_object", "object_pinning", "sticky_immix_non_moving_nursery
 
 # Uncomment the following lines to use mmtk-core from the official repository.
 git = "https://github.com/mmtk/mmtk-core.git"
-rev = "31a78a41f02fc7228780b501c4944ba750e32ee4"
+rev = "6eb1328bfce34a7e0fc4b84fd0b65a849b083e0e"
 
 # Uncomment the following line to use mmtk-core from a local repository.
 #path = "../../mmtk-core"
diff --git a/mmtk/cbindgen.toml b/mmtk/cbindgen.toml
index 84837b8..3a2a920 100644
--- a/mmtk/cbindgen.toml
+++ b/mmtk/cbindgen.toml
@@ -8,8 +8,9 @@ tab_width = 4
 
 usize_is_size_t = true
 
-after_includes = """
+includes = ["ruby/internal/value.h"]
 
+after_includes = """
 typedef struct MMTk_Builder MMTk_Builder;
 typedef struct MMTk_Mutator MMTk_Mutator;
 
@@ -26,6 +27,7 @@ typedef uint32_t MMTk_AllocationSemantics;
 
 [export]
 include = ["HiddenHeader"]
+exclude = ["VALUE"]
 
 [export.rename]
 "MMTKBuilder" = "MMTk_Builder"
diff --git a/mmtk/src/abi.rs b/mmtk/src/abi.rs
index e697dee..f562180 100644
--- a/mmtk/src/abi.rs
+++ b/mmtk/src/abi.rs
@@ -15,6 +15,27 @@ pub const HIDDEN_SIZE_MASK: usize = 0x0000FFFFFFFFFFFF;
 pub const MMTK_WEAK_CONCURRENT_SET_KIND_FSTRING: u8 = 0;
 pub const MMTK_WEAK_CONCURRENT_SET_KIND_GLOBAL_SYMBOLS: u8 = 1;
 
+pub(crate) const RUBY_IMMEDIATE_MASK: usize = 0x07;
+
+#[allow(non_upper_case_globals)] // Match Ruby definition
+pub(crate) const Qundef: VALUE = VALUE(0x24);
+
+#[repr(transparent)]
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+pub struct VALUE(pub usize);
+
+impl VALUE {
+    pub fn is_special_const(&self) -> bool {
+        self.0 == 0 || self.0 & RUBY_IMMEDIATE_MASK != 0
+    }
+}
+
+impl From<ObjectReference> for VALUE {
+    fn from(value: ObjectReference) -> Self {
+        Self(value.to_raw_address().as_usize())
+    }
+}
+
 // An opaque type for the C counterpart.
 #[allow(non_camel_case_types)]
 pub struct st_table;
diff --git a/mmtk/src/api.rs b/mmtk/src/api.rs
index 3867a7f..106fe15 100644
--- a/mmtk/src/api.rs
+++ b/mmtk/src/api.rs
@@ -9,6 +9,7 @@ use crate::abi;
 use crate::abi::HiddenHeader;
 use crate::abi::RawVecOfObjRef;
 use crate::abi::RubyBindingOptions;
+use crate::abi::VALUE;
 use crate::binding;
 use crate::binding::RubyBinding;
 use crate::mmtk;
@@ -421,3 +422,8 @@ pub extern "C" fn mmtk_current_gc_is_nursery() -> bool {
         .generational()
         .is_some_and(|gen| gen.is_current_gc_nursery())
 }
+
+#[no_mangle]
+pub extern "C" fn mmtk_discover_weak_field(field: *mut VALUE) {
+    crate::binding().weak_proc.discover_weak_field(field)
+}
diff --git a/mmtk/src/weak_proc.rs b/mmtk/src/weak_proc.rs
index f9622bc..ea5ab1c 100644
--- a/mmtk/src/weak_proc.rs
+++ b/mmtk/src/weak_proc.rs
@@ -2,12 +2,12 @@ use std::sync::Mutex;
 
 use mmtk::{
     scheduler::{GCWork, GCWorker, WorkBucketStage},
-    util::ObjectReference,
+    util::{Address, ObjectReference},
     vm::ObjectTracerContext,
 };
 
 use crate::{
-    abi::{self, GCThreadTLS},
+    abi::{self, GCThreadTLS, Qundef, VALUE},
     extra_assert, is_mmtk_object_safe, upcalls, Ruby,
 };
 
@@ -27,11 +27,15 @@ pub enum WeakConcurrentSetKind {
     GlobalSymbols = abi::MMTK_WEAK_CONCURRENT_SET_KIND_GLOBAL_SYMBOLS,
 }
 
+pub type FieldType = *mut VALUE;
+
 pub struct WeakProcessor {
     /// Objects that needs `obj_free` called when dying.
     /// If it is a bottleneck, replace it with a lock-free data structure,
     /// or add candidates in batch.
     obj_free_candidates: Mutex<Vec<ObjectReference>>,
+    /// Weak fields discovered during the current GC.
+    weak_fields: Mutex<Vec<FieldType>>,
 }
 
 impl Default for WeakProcessor {
@@ -44,6 +48,7 @@ impl WeakProcessor {
     pub fn new() -> Self {
         Self {
             obj_free_candidates: Mutex::new(Vec::new()),
+            weak_fields: Default::default(),
         }
     }
 
@@ -70,6 +75,28 @@ impl WeakProcessor {
         std::mem::take(obj_free_candidates.as_mut())
     }
 
+    pub fn clear_weak_fields(&self) {
+        let mut weak_fields = self
+            .weak_fields
+            .try_lock()
+            .expect("Should not have contention.");
+        weak_fields.clear();
+    }
+
+    pub fn discover_weak_field(&self, field: FieldType) {
+        let mut weak_fields = self.weak_fields.lock().unwrap();
+        weak_fields.push(field);
+        trace!("Pushed weak field {field:?}");
+    }
+
+    pub fn get_all_weak_fields(&self) -> Vec<FieldType> {
+        let mut weak_fields = self
+            .weak_fields
+            .try_lock()
+            .expect("Should not have contention.");
+        std::mem::take(&mut weak_fields)
+    }
+
     pub fn process_weak_stuff(
         &self,
         worker: &mut GCWorker<Ruby>,
@@ -88,6 +115,7 @@ impl WeakProcessor {
             Box::new(UpdateCCRefinementTable) as _,
             // END: Weak tables
             Box::new(UpdateWbUnprotectedObjectsList) as _,
+            Box::new(UpdateWeakFields) as _,
         ]);
 
         if SPECIALIZE_FSTRING_TABLE_PROCESSING {
@@ -317,3 +345,49 @@ impl Forwardable for ObjectReference {
         self.get_forwarded_object().unwrap_or(*self)
     }
 }
+
+struct UpdateWeakFields;
+
+impl GCWork<Ruby> for UpdateWeakFields {
+    fn do_work(&mut self, _worker: &mut GCWorker<Ruby>, _mmtk: &'static mmtk::MMTK<Ruby>) {
+        let weak_fields = crate::binding().weak_proc.get_all_weak_fields();
+
+        let num_fields = weak_fields.len();
+        let mut live = 0usize;
+        let mut forwarded = 0usize;
+
+        debug!("Updating {num_fields} weak fields...");
+
+        for field in weak_fields {
+            let old_value = unsafe { *field };
+            trace!("  Visiting weak field {field:?} -> {old_value:?}");
+
+            if old_value.is_special_const() {
+                continue;
+            }
+
+            let addr = unsafe { Address::from_usize(old_value.0) };
+            if !addr.is_mapped() {
+                panic!("Field {field:?} value {addr} points to unmapped area");
+            }
+            let Some(old_objref) = mmtk::memory_manager::is_mmtk_object(addr) else {
+                panic!("Field {field:?} value {addr} is an invalid object reference");
+            };
+
+            if old_objref.is_reachable() {
+                live += 1;
+                if let Some(new_objref) = old_objref.get_forwarded_object() {
+                    forwarded += 1;
+                    let new_value = VALUE::from(new_objref);
+                    trace!("    Updated weak field {field:?} to {new_value:?}");
+                    unsafe { *field = new_value };
+                }
+            } else {
+                unsafe { *field = Qundef };
+            }
+        }
+
+        debug!("Updated {num_fields} weak fields.  {live} live, {forwarded} forwarded.");
+        probe!(mmtk_ruby, update_weak_fields, num_fields, live, forwarded);
+    }
+}
diff --git a/tools/tracing/timeline/capture_ruby.bt b/tools/tracing/timeline/capture_ruby.bt
index 0dfa715..0e1472a 100644
--- a/tools/tracing/timeline/capture_ruby.bt
+++ b/tools/tracing/timeline/capture_ruby.bt
@@ -99,3 +99,9 @@ usdt:$MMTK:mmtk_ruby:update_wb_unprotected_objects_list {
         printf("update_wb_unprotected_objects_list,meta,%d,%lu,%lu,%lu\n", tid, nsecs, arg0, arg1);
     }
 }
+
+usdt:$MMTK:mmtk_ruby:update_weak_fields {
+    if (@enable_print) {
+        printf("update_weak_fields,meta,%d,%lu,%lu,%lu,%lu\n", tid, nsecs, arg0, arg1, arg2);
+    }
+}
diff --git a/tools/tracing/timeline/visualize_ruby.py b/tools/tracing/timeline/visualize_ruby.py
index 1298014..62eeaff 100755
--- a/tools/tracing/timeline/visualize_ruby.py
+++ b/tools/tracing/timeline/visualize_ruby.py
@@ -71,6 +71,8 @@ def enrich_meta_extra(log_processor, name, tid, ts, gc, wp, args):
 
             case "weak_cs_par_final":
                 num_entries = int(args[0])
+                if "set_name" not in wp["args"]:
+                    return
                 set_name = wp["args"]["set_name"]
                 gc["args"].setdefault(set_name, {})
                 gc["args"][set_name] |= {
@@ -178,3 +180,14 @@ def enrich_meta_extra(log_processor, name, tid, ts, gc, wp, args):
                         "diff": after - before,
                     },
                 }
+
+            case "update_weak_fields":
+                num_fields, live, forwarded = [int(x) for x in args[0:3]]
+                wp["args"] |= {
+                    "wb_unprotected_objects": {
+                        "num_fields": num_fields,
+                        "live": live,
+                        "forwarded": forwarded,
+                        "cleared": num_fields - live,
+                    },
+                }