[compiler-rt] [scudo] Apply the min release threshold to the group (PR #112014)

[via llvm-commits]

https://github.com/ChiaHungDuan created https://github.com/llvm/llvm-project/pull/112014

For the block smaller than a page size, one block is unlikely to introduce more unused pages (at most 2 if it acrosses the page boundary and both touched pages are unused). So it's better to apply the threshold to reduce the time of scanning groups that can't release any new pages.

>From ae35d1fd3715c08eb076a61eeeb5606b6961a243 Mon Sep 17 00:00:00 2001
From: Chia-hung Duan <chiahungduan at google.com>
Date: Fri, 11 Oct 2024 16:02:12 +0000
Subject: [PATCH] [scudo] Apply the min release threshold to the group

For the block smaller than a page size, one block is unlikely to
introduce more unused pages (at most 2 if it acrosses the page boundary
and both touched pages are unused). So it's better to apply the
threshold to reduce the time of scanning groups that can't release any
new pages.
---
 compiler-rt/lib/scudo/standalone/primary64.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/compiler-rt/lib/scudo/standalone/primary64.h b/compiler-rt/lib/scudo/standalone/primary64.h
index 97188a5ac235cc..1865ed41368e3c 100644
--- a/compiler-rt/lib/scudo/standalone/primary64.h
+++ b/compiler-rt/lib/scudo/standalone/primary64.h
@@ -1492,6 +1492,8 @@ template <typename Config> class SizeClassAllocator64 {
       }
 
       const uptr PushedBytesDelta = BytesInBG - BG->BytesInBGAtLastCheckpoint;
+      if (PushedBytesDelta < getMinReleaseAttemptSize(BlockSize))
+        continue;
 
       // Given the randomness property, we try to release the pages only if the
       // bytes used by free blocks exceed certain proportion of group size. Note