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kernel/vm: when resizing down a VMCache, fill a partial page with zeros

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* factored out file_cache
* fix two gVisor tests: MMapFileTest.ReadSharedTruncatePartialPage
and MMapFileTest.WriteSharedTruncatePartialPage
* fix #19438

Change-Id: Ia7f119478d306ab6d867632e4a5270733f0b29df
Reviewed-on: https://review.haiku-os.org/c/haiku/+/9060
Reviewed-by: waddlesplash <[email protected]>
This commit is contained in:
Jérôme Duval
2025-02-26 17:14:18 +00:00
committed by waddlesplash
parent 30c9648a4f
commit 91880bad83
2 changed files with 11 additions and 14 deletions
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src/system/kernel/cache/file_cache.cpp
Vendored
-14
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@@ -1276,23 +1276,9 @@ file_cache_set_size(void* _cacheRef, off_t newSize)
VMCache* cache = ref->cache;
AutoLocker<VMCache> _(cache);
off_t oldSize = cache->virtual_end;
status_t status = cache->Resize(newSize, VM_PRIORITY_USER);
// Note, the priority doesn't really matter, since this cache doesn't
// reserve any memory.
if (status == B_OK && newSize < oldSize) {
// We may have a new partial page at the end of the cache that must be
// cleared.
uint32 partialBytes = newSize % B_PAGE_SIZE;
if (partialBytes != 0) {
vm_page* page = cache->LookupPage(newSize - partialBytes);
if (page != NULL) {
vm_memset_physical(page->physical_page_number * B_PAGE_SIZE
+ partialBytes, 0, B_PAGE_SIZE - partialBytes);
}
}
}
return status;
}