[base] Implement over-reservation in OS::Allocate on Fuchsia [v8/v8 : main]
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Anton Bikineev (Gerrit)
Jan 29, 2026, 1:20:41 PM (9 days ago) Jan 29
to Michael Lippautz, V8 LUCI CQ, Hannes Payer, cbruni...@chromium.org, mlippau...@chromium.org, oilpan-r...@chromium.org, v8-m...@googlegroups.com, v8-re...@googlegroups.com
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Michael Lippautz (Gerrit)
Jan 29, 2026, 2:05:21 PM (9 days ago) Jan 29
to Anton Bikineev, V8 LUCI CQ, Hannes Payer, cbruni...@chromium.org, mlippau...@chromium.org, oilpan-r...@chromium.org, v8-m...@googlegroups.com, v8-re...@googlegroups.com
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Michael Lippautz voted and added 1 comment![]( "Open in Gerrit")
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File src/base/platform/platform-fuchsia.cc
Line 149, Patchset 4 (Latest):
size_t trim_length, size_t alignment) {Michael Lippautz . unresolved
`target_length`?
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Anton Bikineev (Gerrit)
Jan 29, 2026, 5:16:40 PM (9 days ago) Jan 29
to Michael Lippautz, V8 LUCI CQ, Hannes Payer, cbruni...@chromium.org, mlippau...@chromium.org, oilpan-r...@chromium.org, v8-m...@googlegroups.com, v8-re...@googlegroups.com
Anton Bikineev voted and added 2 comments![]( "Open in Gerrit")
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File src/base/platform/platform-fuchsia.cc
Line 149, Patchset 4:
size_t trim_length, size_t alignment) {Michael Lippautz . resolved
Anton Bikineev`target_length`?
Done, thanks
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V8 LUCI CQ (Gerrit)
Jan 29, 2026, 7:27:36 PM (9 days ago) Jan 29
to Anton Bikineev, Michael Lippautz, Hannes Payer, cbruni...@chromium.org, mlippau...@chromium.org, oilpan-r...@chromium.org, v8-m...@googlegroups.com, v8-re...@googlegroups.com
V8 LUCI CQ submitted the change with unreviewed changes![]( "Open in Gerrit")
Unreviewed changes
4 is the latest approved patch-set.
The change was submitted with unreviewed changes in the following files:
```
The name of the file: src/base/platform/platform-fuchsia.cc
Insertions: 3, Deletions: 3.
@@ -146,12 +146,12 @@
}
void* TrimMapping(const zx::vmar& vmar, void* base_address, size_t base_length,
- size_t trim_length, size_t alignment) {
+ size_t target_length, size_t alignment) {
uintptr_t base = reinterpret_cast<uintptr_t>(base_address);
uintptr_t new_base = (base + alignment - 1) & ~(alignment - 1);
DCHECK_GE(new_base, base);
size_t pre_slack = new_base - base;
- size_t post_slack = base_length - pre_slack - trim_length;
+ size_t post_slack = base_length - pre_slack - target_length;
DCHECK_LE(pre_slack, base_length);
DCHECK_LE(post_slack, base_length);
@@ -159,7 +159,7 @@
vmar.unmap(base, pre_slack);
}
if (post_slack) {
- vmar.unmap(new_base + trim_length, post_slack);
+ vmar.unmap(new_base + target_length, post_slack);
}
return reinterpret_cast<void*>(new_base);
}
```
Change information
Commit message:
[base] Implement over-reservation in OS::Allocate on Fuchsia
This CL implements over-reservation logic in CreateAndMapVmo (used by
OS::Allocate) to support memory allocations with alignment larger than
4GB (e.g. 32GB for CppGC Cage). Fuchsia's VMAR mapping does not support
alignment > 4GB natively. We overallocate (size + alignment), map it,
find the aligned address, and unmap the head and tail.
Bug: 454026468
Change-Id: I319452e7779826557d208507fec8ee33a6ad0fb4
Commit-Queue: Anton Bikineev <biki...@chromium.org>
Reviewed-by: Michael Lippautz <mlip...@chromium.org>
Cr-Commit-Position: refs/heads/main@{#104990}
Files:
- M src/base/platform/platform-fuchsia.cc
- M src/heap/cppgc/caged-heap.cc
Change size: M
Delta: 2 files changed, 52 insertions(+), 7 deletions(-)
Branch: refs/heads/main
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Code-Review: +1 by Michael Lippautz
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