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Expose notify_using_readonly

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This exposes a readonly notify using, so that the underlying platform
can map the range of pages readonly into the application.  This improves
performance of external pointer on platforms that support lazy commit
of pages as it can access anything in the range.
This commit is contained in:
Matthew Parkinson
2021-09-23 15:56:59 +01:00
committed by Matthew Parkinson
parent 0af1ee3bef
commit b4efc40aa6
3 changed files with 45 additions and 11 deletions
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27
src/backend/pagemap.h
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@@ -159,7 +159,7 @@ namespace snmalloc
#ifdef SNMALLOC_CHECK_CLIENT
// Allocate a power of two extra to allow the placement of the
// pagemap be difficult to guess.
size_t additional_size = bits::next_pow2(REQUIRED_SIZE) * 2;
size_t additional_size = bits::next_pow2(REQUIRED_SIZE) * 4;
size_t request_size = REQUIRED_SIZE + additional_size;
#else
size_t request_size = REQUIRED_SIZE;
@@ -178,6 +178,18 @@ namespace snmalloc
size_t offset = get_entropy64<PAL>() & (additional_size - sizeof(T));
auto new_body =
reinterpret_cast<T*>(pointer_offset(new_body_untyped, offset));
if constexpr (pal_supports<LazyCommit, PAL>)
{
void* start_page = pointer_align_down<OS_PAGE_SIZE>(new_body);
void* end_page = pointer_align_up<OS_PAGE_SIZE>(
pointer_offset(new_body, REQUIRED_SIZE));
// Only commit readonly memory for this range, if the platform supports
// lazy commit. Otherwise, this would be a lot of memory to have
// mapped.
PAL::notify_using_readonly(
start_page, pointer_diff(start_page, end_page));
}
#else
auto new_body = reinterpret_cast<T*>(new_body_untyped);
#endif
@@ -243,15 +255,10 @@ namespace snmalloc
p = p - base;
}
// This means external pointer on Windows will be slow.
// TODO: With SNMALLOC_CHECK_CLIENT we should map that region read-only,
// not no-access, but this requires a PAL change.
if constexpr (
potentially_out_of_range
#ifndef SNMALLOC_CHECK_CLIENT
&& !pal_supports<LazyCommit, PAL>
#endif
)
// If this is potentially_out_of_range, then the pages will not have
// been mapped. With Lazy commit they will at least be mapped read-only
// Note that: this means external pointer on Windows will be slow.
if constexpr (potentially_out_of_range && !pal_supports<LazyCommit, PAL>)
{
register_range(p, 1);
}