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[184.145.4.219]) by smtp.gmail.com with ESMTPSA id c141sm950456qke.12.2021.05.07.08.06.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 07 May 2021 08:06:03 -0700 (PDT) From: Peter Xu To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Jan Kara , John Hubbard , peterx@redhat.com, Linus Torvalds , Michal Hocko , Kirill Tkhai , Kirill Shutemov , Oleg Nesterov , Andrew Morton , Jann Horn , Andrea Arcangeli , Jason Gunthorpe , Matthew Wilcox , Hugh Dickins Subject: [PATCH v2 3/3] mm: gup: pack has_pinned in MMF_HAS_PINNED Date: Fri, 7 May 2021 11:05:53 -0400 Message-Id: <20210507150553.208763-4-peterx@redhat.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210507150553.208763-1-peterx@redhat.com> References: <20210507150553.208763-1-peterx@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="US-ASCII" X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: DCFEA135 Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=ic1qgjGV; spf=none (imf29.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 216.205.24.124) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Stat-Signature: oj5oqoaheyditznf7b1m314f9s414jsg Received-SPF: none (redhat.com>: No applicable sender policy available) receiver=imf29; identity=mailfrom; envelope-from=""; helo=us-smtp-delivery-124.mimecast.com; client-ip=216.205.24.124 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1620399964-983564 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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_str= uct *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 =3D 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; =20 - if (!atomic_read(&vma->vm_mm->has_pinned)) + if (!test_bit(MMF_HAS_PINNED, &vma->vm_mm->flags)) return false; =20 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; =20 - /** - * @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/coredum= p.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 ei= ther + * replaced in the future by mm.pinned_vm when it becomes stable, or gro= w into + * a counter on its own. We're aggresive on this bit for now: even if th= e + * pinned pages were unpinned later on, we'll still keep this bit set fo= r 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) =20 #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 =3D 0; mm->locked_vm =3D 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); =20 +/* + * Set the MMF_HAS_PINNED if not set yet; after set it'll be there for t= he 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 !=3D 1); } =20 - 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); =20 /* * FOLL_PIN and FOLL_GET are mutually exclusive. Traditional behavior @@ -2617,8 +2628,8 @@ static int internal_get_user_pages_fast(unsigned lo= ng start, FOLL_FAST_ONLY))) return -EINVAL; =20 - 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); =20 if (!(gup_flags & FOLL_FAST_ONLY)) might_lock_read(¤t->mm->mmap_lock); --=20 2.31.1