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From: Kent Overstreet To: Shakeel Butt Cc: 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-Migadu-Flow: FLOW_OUT X-Stat-Signature: yjpzd63kxi5i4sherxsgd71hpeesteth X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 23353140011 X-HE-Tag: 1747751291-559438 X-HE-Meta: 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 /WGhR5Z4 k+Gj6W6R+iU/kQHczU+btgjZX8uPwP1NZ54B0KyTV56TeMEN1X6Z2aU8zbbDjggxAewWMtTPC5Niw/cJu+EpY7BK5dufFp25I1DvD3AODzOzEo4qImaWXOvyrYarLvMe4xW4FL/wTlmdpkFrNS9TpF6+aP+89kWM8/rvV+tA8goazdE+ckBWU6aFyBordlWeiCfgGt787G0xK6gCmd0ocR0oqFxeIXtSTlCL5Lze/0/Y5b7OB8Kp+XeJw8XaMwgKkxoKMbZiLM4JmA5GrMYn9GyGNDMsvFVTnHiEhcDg2rKWeLF2Q+Z6mYj/Hay13lWQu5ISaYSoWzFR5iLw= 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 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...