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Wed, 09 Jun 2021 11:39:33 +0000 From: Vlastimil Babka To: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Christoph Lameter , David Rientjes , Pekka Enberg , Joonsoo Kim Cc: Sebastian Andrzej Siewior , Thomas Gleixner , Mel Gorman , Jesper Dangaard Brouer , Peter Zijlstra , Jann Horn , Vlastimil Babka Subject: [RFC v2 12/34] mm, slub: move disabling/enabling irqs to ___slab_alloc() Date: Wed, 9 Jun 2021 13:38:41 +0200 Message-Id: <20210609113903.1421-13-vbabka@suse.cz> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210609113903.1421-1-vbabka@suse.cz> References: <20210609113903.1421-1-vbabka@suse.cz> MIME-Version: 1.0 X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 7468A200107C X-Stat-Signature: 8zahtgx49gxsmbnnadfg69xekdarxjfn Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=2FEH2m+j; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=LB74xd0R; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=2FEH2m+j; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=LB74xd0R; dmarc=none; spf=pass (imf11.hostedemail.com: domain of vbabka@suse.cz designates 195.135.220.29 as permitted sender) smtp.mailfrom=vbabka@suse.cz X-HE-Tag: 1623238770-271504 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: Currently __slab_alloc() disables irqs around the whole ___slab_alloc(). = This includes cases where this is not needed, such as when the allocation ends= up in the page allocator and has to awkwardly enable irqs back based on gfp fla= gs. Also the whole kmem_cache_alloc_bulk() is executed with irqs disabled eve= n when it hits the __slab_alloc() slow path, and long periods with disabled inte= rrupts are undesirable. As a first step towards reducing irq disabled periods, move irq handling = into ___slab_alloc(). Callers will instead prevent the s->cpu_slab percpu poin= ter from becoming invalid via get_cpu_ptr(), thus preempt_disable(). This doe= s not protect against modification by an irq handler, which is still done by di= sabled irq for most of ___slab_alloc(). As a small immediate benefit, slab_out_of_memory() from ___slab_alloc() is now called with irqs enabled= . kmem_cache_alloc_bulk() disables irqs for its fastpath and then re-enable= s them before calling ___slab_alloc(), which then disables them at its discretio= n. The whole kmem_cache_alloc_bulk() operation also disables preemption. When ___slab_alloc() calls new_slab() to allocate a new page, re-enable preemption, because new_slab() will re-enable interrupts in contexts that= allow blocking (this will be improved by later patches). The patch itself will thus increase overhead a bit due to disabled preemp= tion and increased disabling/enabling irqs in kmem_cache_alloc_bulk(), but tha= t will be gradually improved in the following patches. Signed-off-by: Vlastimil Babka --- mm/slub.c | 32 ++++++++++++++++++++++---------- 1 file changed, 22 insertions(+), 10 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 6d6a9a69db8a..4800d768d0d3 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2610,7 +2610,7 @@ static inline void *get_freelist(struct kmem_cache = *s, struct page *page) * we need to allocate a new slab. This is the slowest path since it inv= olves * a call to the page allocator and the setup of a new slab. * - * Version of __slab_alloc to use when we know that interrupts are + * Version of __slab_alloc to use when we know that preemption is * already disabled (which is the case for bulk allocation). */ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int nod= e, @@ -2618,9 +2618,11 @@ static void *___slab_alloc(struct kmem_cache *s, g= fp_t gfpflags, int node, { void *freelist; struct page *page; + unsigned long flags; =20 stat(s, ALLOC_SLOWPATH); =20 + local_irq_save(flags); page =3D c->page; if (!page) { /* @@ -2683,6 +2685,7 @@ static void *___slab_alloc(struct kmem_cache *s, gf= p_t gfpflags, int node, VM_BUG_ON(!c->page->frozen); c->freelist =3D get_freepointer(s, freelist); c->tid =3D next_tid(c->tid); + local_irq_restore(flags); return freelist; =20 new_slab: @@ -2700,14 +2703,16 @@ static void *___slab_alloc(struct kmem_cache *s, = gfp_t gfpflags, int node, goto check_new_page; } =20 + put_cpu_ptr(s->cpu_slab); page =3D new_slab(s, gfpflags, node); + c =3D get_cpu_ptr(s->cpu_slab); =20 if (unlikely(!page)) { + local_irq_restore(flags); slab_out_of_memory(s, gfpflags, node); return NULL; } =20 - c =3D raw_cpu_ptr(s->cpu_slab); if (c->page) flush_slab(s, c); =20 @@ -2747,31 +2752,33 @@ static void *___slab_alloc(struct kmem_cache *s, = gfp_t gfpflags, int node, return_single: =20 deactivate_slab(s, page, get_freepointer(s, freelist), c); + local_irq_restore(flags); return freelist; } =20 /* - * Another one that disabled interrupt and compensates for possible - * cpu changes by refetching the per cpu area pointer. + * A wrapper for ___slab_alloc() for contexts where preemption is not ye= t + * disabled. Compensates for possible cpu changes by refetching the per = cpu area + * pointer. */ static void *__slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node= , unsigned long addr, struct kmem_cache_cpu *c) { void *p; - unsigned long flags; =20 - local_irq_save(flags); #ifdef CONFIG_PREEMPTION /* * We may have been preempted and rescheduled on a different - * cpu before disabling interrupts. Need to reload cpu area + * cpu before disabling preemption. Need to reload cpu area * pointer. */ - c =3D this_cpu_ptr(s->cpu_slab); + c =3D get_cpu_ptr(s->cpu_slab); #endif =20 p =3D ___slab_alloc(s, gfpflags, node, addr, c); - local_irq_restore(flags); +#ifdef CONFIG_PREEMPTION + put_cpu_ptr(s->cpu_slab); +#endif return p; } =20 @@ -3291,8 +3298,8 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp= _t flags, size_t size, * IRQs, which protects against PREEMPT and interrupts * handlers invoking normal fastpath. */ + c =3D get_cpu_ptr(s->cpu_slab); local_irq_disable(); - c =3D this_cpu_ptr(s->cpu_slab); =20 for (i =3D 0; i < size; i++) { void *object =3D kfence_alloc(s, s->object_size, flags); @@ -3313,6 +3320,8 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp= _t flags, size_t size, */ c->tid =3D next_tid(c->tid); =20 + local_irq_enable(); + /* * Invoking slow path likely have side-effect * of re-populating per CPU c->freelist @@ -3325,6 +3334,8 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp= _t flags, size_t size, c =3D this_cpu_ptr(s->cpu_slab); maybe_wipe_obj_freeptr(s, p[i]); =20 + local_irq_disable(); + continue; /* goto for-loop */ } c->freelist =3D get_freepointer(s, object); @@ -3333,6 +3344,7 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp= _t flags, size_t size, } c->tid =3D next_tid(c->tid); local_irq_enable(); + put_cpu_ptr(s->cpu_slab); =20 /* * memcg and kmem_cache debug support and memory initialization. --=20 2.31.1