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[95.193.69.199]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-550e6f35205sm2442624e87.95.2025.05.20.10.57.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 May 2025 10:57:13 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Tue, 20 May 2025 19:57:10 +0200 To: Kent Overstreet Cc: Uladzislau Rezki , Shakeel Butt , Usama Arif , Andrew Morton , surenb@google.com, hannes@cmpxchg.org, vlad.wing@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH 1/2] mm: slub: allocate slab object extensions non-contiguously Message-ID: References: <20250520122547.1317050-1-usamaarif642@gmail.com> <3divtzm4iapcxwbzxlmfmg3gus75n3rqh43vkjnog456jm2k34@f3rpzvcfk3p6> <6d015d91-e74c-48b3-8bc3-480980a74f9b@gmail.com> <22oihuvcrh5sg3urocw6wbop2v5yni7zinuhywbz7glsee4yoa@gzi5v5fcggdl> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: zsgbqktkfkozmxrgrys8a5jc5m1d119q X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 79BE1180016 X-HE-Tag: 1747763836-102093 X-HE-Meta: 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 8k7cuAJV 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 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: List-Subscribe: List-Unsubscribe: On Tue, May 20, 2025 at 01:47:54PM -0400, Kent Overstreet wrote: > On Tue, May 20, 2025 at 07:44:49PM +0200, Uladzislau Rezki wrote: > > On Tue, May 20, 2025 at 10:28:06AM -0400, Kent Overstreet wrote: > > > On Tue, May 20, 2025 at 07:24:40AM -0700, Shakeel Butt wrote: > > > > On Tue, May 20, 2025 at 10:01:27AM -0400, Kent Overstreet wrote: > > > > > On Tue, May 20, 2025 at 02:46:14PM +0100, Usama Arif wrote: > > > > > > > > > > > > > > > > > > On 20/05/2025 14:44, Kent Overstreet wrote: > > > > > > > On Tue, May 20, 2025 at 01:25:46PM +0100, Usama Arif wrote: > > > > > > >> When memory allocation profiling is running on memory bound services, > > > > > > >> allocations greater than order 0 for slab object extensions can fail, > > > > > > >> for e.g. zs_handle zswap slab which will be 512 objsperslab x 16 bytes > > > > > > >> per slabobj_ext (order 1 allocation). Use kvcalloc to improve chances > > > > > > >> of the allocation being successful. > > > > > > >> > > > > > > >> Signed-off-by: Usama Arif > > > > > > >> Reported-by: Vlad Poenaru > > > > > > >> Closes: https://lore.kernel.org/all/17fab2d6-5a74-4573-bcc3-b75951508f0a@gmail.com/ > > > > > > >> --- > > > > > > >> mm/slub.c | 2 +- > > > > > > >> 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > >> > > > > > > >> diff --git a/mm/slub.c b/mm/slub.c > > > > > > >> index dc9e729e1d26..bf43c403ead2 100644 > > > > > > >> --- a/mm/slub.c > > > > > > >> +++ b/mm/slub.c > > > > > > >> @@ -1989,7 +1989,7 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, > > > > > > >> gfp &= ~OBJCGS_CLEAR_MASK; > > > > > > >> /* Prevent recursive extension vector allocation */ > > > > > > >> gfp |= __GFP_NO_OBJ_EXT; > > > > > > >> - vec = kcalloc_node(objects, sizeof(struct slabobj_ext), gfp, > > > > > > >> + vec = kvcalloc_node(objects, sizeof(struct slabobj_ext), gfp, > > > > > > >> slab_nid(slab)); > > > > > > > > > > > > > > And what's the latency going to be on a vmalloc() allocation when we're > > > > > > > low on memory? > > > > > > > > > > > > Would it not be better to get the allocation slighly slower than to not get > > > > > > it at all? > > > > > > > > > > Our behaviour when thrashing sucks, we don't want to do anything to make > > > > > that worse. > > > > > > > > > > There's also the fact that vmalloc doesn't correctly respect gfp flags, > > > > > so until that gets fixed this doesn't work at all. > > > > > > > > Which gfp flags vmalloc is not respecting today? > > > > > > GFP_NOWAIT. > > > > > > As to why, you'd better ask Michal Hocko... > > > > > It is mainly due to pte_alloc_one_kernel(), it uses the GFP_KERNEL > > > > #define GFP_PGTABLE_KERNEL (GFP_KERNEL | __GFP_ZERO) > > > > to get a new pte entry. > > > > I think we can fix it. For example if we populate some region and allocate > > there for NOWAIT. But there are of course can be other hidden problems. > > No, PF_MEMALLOC flags allow for passing most of gfp flags for pte > allocation. > It is hard-coded: static inline pte_t *__pte_alloc_one_kernel_noprof(struct mm_struct *mm) { struct ptdesc *ptdesc = pagetable_alloc_noprof(GFP_PGTABLE_KERNEL & ~__GFP_HIGHMEM, 0); if (!ptdesc) return NULL; return ptdesc_address(ptdesc); } -- Uladzislau Rezki