| Message ID | 20200416220130.13343-1-willy@infradead.org (mailing list archive) |
|---|---|
| Headers | show |
| Series | Make PageWriteback use the PageLocked optimisation | expand |
Hi Matthew, On Fri, Apr 17, 2020 at 12:01 AM Matthew Wilcox <willy@infradead.org> wrote: > From: "Matthew Wilcox (Oracle)" <willy@infradead.org> > PageWaiters is used by PageWriteback and PageLocked (and no other page > flags), so it makes sense to use the same codepaths that have already been > optimised for PageLocked, even if there's probably no real performance > benefit to be had. > > Unfortunately, clear_bit_unlock_is_negative_byte() isn't present on every > architecture, and the default implementation is only available in filemap.c > while I want to use it in page-writeback.c. Rather than move the default > implementation to a header file, I've done optimised implementations for > alpha and ia64. I can't figure out optimised implementations for m68k, > mips, riscv and s390, so I've just replicated the effect of the generic > implementation in them. I leave it to the experts to fix that (... or > convert over to using asm-generic/bitops/lock.h ...) > > v3: > - Added implementations of clear_bit_unlock_is_negative_byte() > to architectures which need it I have two questions here? 1. Why not implement arch_clear_bit_unlock_is_negative_byte() instead, so the kasan check in asm-generic is used everywhere? 2. Why not add the default implementation to include/asm-generic/bitops/instrumented-lock.h, in case an arch_*() variant is not provided yet? Note that you did 1 for s390. Thanks! Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
On Fri, Apr 17, 2020 at 09:28:14AM +0200, Geert Uytterhoeven wrote: > On Fri, Apr 17, 2020 at 12:01 AM Matthew Wilcox <willy@infradead.org> wrote: > > v3: > > - Added implementations of clear_bit_unlock_is_negative_byte() > > to architectures which need it > > I have two questions here? > 1. Why not implement arch_clear_bit_unlock_is_negative_byte() > instead, so the kasan check in asm-generic is used everywhere? That would be a larger change. As I understand it (and I may misunderstand it), I would need to rename all the clear_bit(), __clear_bit(), change_bit(), ... functions to have an 'arch_' prefix and then include instrumented-lock.h > 2. Why not add the default implementation to > include/asm-generic/bitops/instrumented-lock.h, in case an arch_*() > variant is not provided yet? > > Note that you did 1 for s390. Well, s390 already uses instrumented-lock.h so I followed along with what they're doing. I don't think instrumented-lock.h is used at all on these other architectures, but the whole bitops header files are such a mess that I could easily have built a completely wrong mental model of what's going on.
From: "Matthew Wilcox (Oracle)" <willy@infradead.org> PageWaiters is used by PageWriteback and PageLocked (and no other page flags), so it makes sense to use the same codepaths that have already been optimised for PageLocked, even if there's probably no real performance benefit to be had. Unfortunately, clear_bit_unlock_is_negative_byte() isn't present on every architecture, and the default implementation is only available in filemap.c while I want to use it in page-writeback.c. Rather than move the default implementation to a header file, I've done optimised implementations for alpha and ia64. I can't figure out optimised implementations for m68k, mips, riscv and s390, so I've just replicated the effect of the generic implementation in them. I leave it to the experts to fix that (... or convert over to using asm-generic/bitops/lock.h ...) v3: - Added implementations of clear_bit_unlock_is_negative_byte() to architectures which need it v2: Rebased to 5.7-rc1 - Split up patches better - Moved the BUG() from end_page_writeback() to __clear_page_writeback() as requested by Jan Kara. - Converted the BUG() to WARN_ON() - Removed TestClearPageWriteback Matthew Wilcox (Oracle) (11): alpha: Add clear_bit_unlock_is_negative_byte implementation ia64: Add clear_bit_unlock_is_negative_byte implementation m68k: Add clear_bit_unlock_is_negative_byte implementation mips: Add clear_bit_unlock_is_negative_byte implementation riscv: Add clear_bit_unlock_is_negative_byte implementation s390: Add clear_bit_unlock_is_negative_byte implementation mm: Remove definition of clear_bit_unlock_is_negative_byte mm: Move PG_writeback into the bottom byte mm: Convert writeback BUG to WARN_ON mm: Use clear_bit_unlock_is_negative_byte for PageWriteback mm: Remove TestClearPageWriteback arch/alpha/include/asm/bitops.h | 23 ++++++++++++++++++ arch/ia64/include/asm/bitops.h | 20 ++++++++++++++++ arch/m68k/include/asm/bitops.h | 7 ++++++ arch/mips/include/asm/bitops.h | 7 ++++++ arch/riscv/include/asm/bitops.h | 7 ++++++ arch/s390/include/asm/bitops.h | 9 +++++++ include/linux/page-flags.h | 8 +++---- mm/filemap.c | 41 ++++---------------------------- mm/page-writeback.c | 42 ++++++++++++++++++++------------- 9 files changed, 107 insertions(+), 57 deletions(-)