From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-ej1-f50.google.com (mail-ej1-f50.google.com [209.85.218.50]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D797D71 for ; Wed, 12 May 2021 09:50:09 +0000 (UTC) Received: by mail-ej1-f50.google.com with SMTP id c22so5947115ejd.12 for ; Wed, 12 May 2021 02:50:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=GUt7kPgBJMN4yeVeOkrnQPhryLYrZDgrYjGs4lAolt0=; b=ny8mv3++m4i3B4RuxmYCDHFPZlicowKuAS8DYTUdpV+/w8b0YH+X604s0wwq/lCGyb DR8eoBJ0erFDUQLA3OXISUEEsuXm3Qn6YXjhTCR9ohPlny+kEmsvNAJoH0I2u/byDzPQ 1cSY5VjBECxKDVWnjy9nRoKB4cnb29GlY8tXoxiWTo+fai6eDqa8D5TiL7FfFE8tXE9c nbVvECz0MehXQkRQYmIoF6PlwprkF+LxUuReOEYb8HjkkxGSEMycPm1A2QSUSFSmusdu gDaoqJ4t9oDulXcRivGVbe7vO3W2gkOmCqV6bOi2QPctaaIzFy3z8GZpXikvFW9XOCcy isrw== X-Google-DKIM-Signature: v=1; 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charset="UTF-8" On Fri, 7 May 2021 at 20:36, Peter Xu wrote: > > From: Andrea Arcangeli > > has_pinned 32bit can be packed in the MMF_HAS_PINNED bit as a noop > cleanup. > > Any atomic_inc/dec to the mm cacheline shared by all threads in > pin-fast would reintroduce a loss of SMP scalability to pin-fast, so > there's no future potential usefulness to keep an atomic in the mm for > this. > > set_bit(MMF_HAS_PINNED) will be theoretically a bit slower than > WRITE_ONCE (atomic_set is equivalent to WRITE_ONCE), but the set_bit > (just like atomic_set after this commit) has to be still issued only > once per "mm", so the difference between the two will be lost in the > noise. > > will-it-scale "mmap2" shows no change in performance with enterprise > config as expected. > > will-it-scale "pin_fast" retains the > 4000% SMP scalability > performance improvement against upstream as expected. > > This is a noop as far as overall performance and SMP scalability are > concerned. > > Signed-off-by: Andrea Arcangeli > [peterx: Fix build for task_mmu.c, introduce mm_set_has_pinned_flag, fix > comment here and there] > Signed-off-by: Peter Xu > --- > fs/proc/task_mmu.c | 2 +- > include/linux/mm.h | 2 +- > include/linux/mm_types.h | 10 ---------- > include/linux/sched/coredump.h | 8 ++++++++ > kernel/fork.c | 1 - > mm/gup.c | 19 +++++++++++++++---- > 6 files changed, 25 insertions(+), 17 deletions(-) > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index 4c95cc57a66a8..6144571942db9 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -1049,7 +1049,7 @@ static inline bool pte_is_pinned(struct vm_area_struct *vma, unsigned long addr, > return false; > if (!is_cow_mapping(vma->vm_flags)) > return false; > - if (likely(!atomic_read(&vma->vm_mm->has_pinned))) > + if (likely(!test_bit(MMF_HAS_PINNED, &vma->vm_mm->flags))) > return false; > page = vm_normal_page(vma, addr, pte); > if (!page) > diff --git a/include/linux/mm.h b/include/linux/mm.h > index d6790ab0cf575..94dc84f6d8658 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1331,7 +1331,7 @@ static inline bool page_needs_cow_for_dma(struct vm_area_struct *vma, > if (!is_cow_mapping(vma->vm_flags)) > return false; > > - if (!atomic_read(&vma->vm_mm->has_pinned)) > + if (!test_bit(MMF_HAS_PINNED, &vma->vm_mm->flags)) > return false; > > return page_maybe_dma_pinned(page); > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index 6613b26a88946..15d79858fadbd 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -435,16 +435,6 @@ struct mm_struct { > */ > atomic_t mm_count; > > - /** > - * @has_pinned: Whether this mm has pinned any pages. This can > - * be either replaced in the future by @pinned_vm when it > - * becomes stable, or grow into a counter on its own. We're > - * aggresive on this bit now - even if the pinned pages were > - * unpinned later on, we'll still keep this bit set for the > - * lifecycle of this mm just for simplicity. > - */ > - atomic_t has_pinned; > - > /** > * @write_protect_seq: Locked when any thread is write > * protecting pages mapped by this mm to enforce a later COW, > diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h > index dfd82eab29025..4d9e3a6568758 100644 > --- a/include/linux/sched/coredump.h > +++ b/include/linux/sched/coredump.h > @@ -73,6 +73,14 @@ static inline int get_dumpable(struct mm_struct *mm) > #define MMF_OOM_VICTIM 25 /* mm is the oom victim */ > #define MMF_OOM_REAP_QUEUED 26 /* mm was queued for oom_reaper */ > #define MMF_MULTIPROCESS 27 /* mm is shared between processes */ > +/* > + * MMF_HAS_PINNED: Whether this mm has pinned any pages. This can be either > + * replaced in the future by mm.pinned_vm when it becomes stable, or grow into > + * a counter on its own. We're aggresive on this bit for now: even if the > + * pinned pages were unpinned later on, we'll still keep this bit set for the > + * lifecycle of this mm, just for simplicity. > + */ > +#define MMF_HAS_PINNED 28 /* FOLL_PIN has run, never cleared */ > #define MMF_DISABLE_THP_MASK (1 << MMF_DISABLE_THP) > > #define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK |\ > diff --git a/kernel/fork.c b/kernel/fork.c > index 502dc046fbc62..a71e73707ef59 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -1026,7 +1026,6 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p, > mm_pgtables_bytes_init(mm); > mm->map_count = 0; > mm->locked_vm = 0; > - atomic_set(&mm->has_pinned, 0); > atomic64_set(&mm->pinned_vm, 0); > memset(&mm->rss_stat, 0, sizeof(mm->rss_stat)); > spin_lock_init(&mm->page_table_lock); > diff --git a/mm/gup.c b/mm/gup.c > index 9933bc5c2eff2..bb130723a6717 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -1270,6 +1270,17 @@ int fixup_user_fault(struct mm_struct *mm, > } > EXPORT_SYMBOL_GPL(fixup_user_fault); > > +/* > + * Set the MMF_HAS_PINNED if not set yet; after set it'll be there for the mm's > + * lifecycle. Avoid setting the bit unless necessary, or it might cause write > + * cache bouncing on large SMP machines for concurrent pinned gups. > + */ > +static inline void mm_set_has_pinned_flag(unsigned long *mm_flags) > +{ > + if (!test_bit(MMF_HAS_PINNED, mm_flags)) > + set_bit(MMF_HAS_PINNED, mm_flags); > +} > + > /* > * Please note that this function, unlike __get_user_pages will not > * return 0 for nr_pages > 0 without FOLL_NOWAIT > @@ -1292,8 +1303,8 @@ static __always_inline long __get_user_pages_locked(struct mm_struct *mm, > BUG_ON(*locked != 1); > } > > - if ((flags & FOLL_PIN) && !atomic_read(&mm->has_pinned)) > - atomic_set(&mm->has_pinned, 1); > + if (flags & FOLL_PIN) > + mm_set_has_pinned_flag(&mm->flags); > > /* > * FOLL_PIN and FOLL_GET are mutually exclusive. Traditional behavior > @@ -2617,8 +2628,8 @@ static int internal_get_user_pages_fast(unsigned long start, > FOLL_FAST_ONLY))) > return -EINVAL; > > - if ((gup_flags & FOLL_PIN) && !atomic_read(¤t->mm->has_pinned)) > - atomic_set(¤t->mm->has_pinned, 1); > + if (gup_flags & FOLL_PIN) > + mm_set_has_pinned_flag(¤t->mm->flags); Linux next tag next-20210512 builds failed on arm, riscv, mips and sh for the tinyconfig and allnoconfig due this patch. arm, mips, riscv and sh (tinyconfig) with gcc-8 arm, mips, riscv and sh (allnoconfig) with gcc-8 arm, mips, riscv and sh (tinyconfig) with gcc-9 arm, mips, riscv and sh (allnoconfig) with gcc-9 arm, mips, riscv and sh (tinyconfig) with gcc-10 arm, mips, riscv and sh (allnoconfig) with gcc-10 mm/gup.c: In function 'internal_get_user_pages_fast': mm/gup.c:2698:3: error: implicit declaration of function 'mm_set_has_pinned_flag' [-Werror=implicit-function-declaration] 2698 | mm_set_has_pinned_flag(¤t->mm->flags); | ^~~~~~~~~~~~~~~~~~~~~~ cc1: some warnings being treated as errors make[2]: *** [/builds/linux/scripts/Makefile.build:273: mm/gup.o] Error 1 Reported-by: Naresh Kamboju #regzb introduced: 354a2e3604e2 ("mm: gup: pack has_pinned in MMF_HAS_PINNED") Build url: https://gitlab.com/Linaro/lkft/mirrors/next/linux-next/-/jobs/1255567072#L315 -- Linaro LKFT https://lkft.linaro.org