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mm: add folio_xor_flags_has_waiters()

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Optimise folio_end_read() by setting the uptodate bit at the same time we
clear the unlock bit.  This saves at least one memory barrier and one
write-after-write hazard.

Link: https://lkml.kernel.org/r/20231004165317.1061855-16-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Matthew Wilcox (Oracle) 2023-10-04 17:53:15 +01:00 • committed by Andrew Morton
parent f12fb73b74
commit 0410cd844e
2 changed files with 30 additions and 3 deletions
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19
include/linux/page-flags.h
View file

@ -692,6 +692,25 @@ TESTPAGEFLAG_FALSE(Ksm, ksm)
u64 stable_page_flags(struct page *page); u64 stable_page_flags(struct page *page);
/**
* folio_xor_flags_has_waiters - Change some folio flags.
* @folio: The folio.
* @mask: Bits set in this word will be changed.
*
* This must only be used for flags which are changed with the folio
* lock held. For example, it is unsafe to use for PG_dirty as that
* can be set without the folio lock held. It can also only be used
* on flags which are in the range 0-6 as some of the implementations
* only affect those bits.
*
* Return: Whether there are tasks waiting on the folio.
*/
static inline bool folio_xor_flags_has_waiters(struct folio *folio,
unsigned long mask)
{
return xor_unlock_is_negative_byte(mask, folio_flags(folio, 0));
}
/** /**
* folio_test_uptodate - Is this folio up to date? * folio_test_uptodate - Is this folio up to date?
* @folio: The folio. * @folio: The folio.

14
mm/filemap.c
View file

@ -1497,7 +1497,7 @@ void folio_unlock(struct folio *folio)
BUILD_BUG_ON(PG_waiters != 7); BUILD_BUG_ON(PG_waiters != 7);
BUILD_BUG_ON(PG_locked > 7); BUILD_BUG_ON(PG_locked > 7);
VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio); VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
if (xor_unlock_is_negative_byte(1 << PG_locked, folio_flags(folio, 0))) if (folio_xor_flags_has_waiters(folio, 1 << PG_locked))
folio_wake_bit(folio, PG_locked); folio_wake_bit(folio, PG_locked);
} }
EXPORT_SYMBOL(folio_unlock); EXPORT_SYMBOL(folio_unlock);
@ -1518,9 +1518,17 @@ EXPORT_SYMBOL(folio_unlock);
*/ */
void folio_end_read(struct folio *folio, bool success) void folio_end_read(struct folio *folio, bool success)
{ {
unsigned long mask = 1 << PG_locked;
/* Must be in bottom byte for x86 to work */
BUILD_BUG_ON(PG_uptodate > 7);
VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
VM_BUG_ON_FOLIO(folio_test_uptodate(folio), folio);
if (likely(success)) if (likely(success))
folio_mark_uptodate(folio); mask |= 1 << PG_uptodate;
folio_unlock(folio); if (folio_xor_flags_has_waiters(folio, mask))
folio_wake_bit(folio, PG_locked);
} }
EXPORT_SYMBOL(folio_end_read); EXPORT_SYMBOL(folio_end_read);