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Wed, 09 Apr 2025 00:35:07 -0700 (PDT) Received: from localhost ([193.86.92.181]) by smtp.gmail.com with UTF8SMTPSA id a640c23a62f3a-acaa1ccc157sm48729066b.142.2025.04.09.00.35.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 09 Apr 2025 00:35:07 -0700 (PDT) Date: Wed, 9 Apr 2025 09:35:06 +0200 From: Michal Hocko To: Dave Chinner , Andrew Morton Cc: Shakeel Butt , Yafang Shao , Harry Yoo , Kees Cook , joel.granados@kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Josef Bacik , linux-mm@kvack.org, Vlastimil Babka Subject: Re: [PATCH] mm: kvmalloc: make kmalloc fast path real fast path Message-ID: References: <20250401073046.51121-1-laoar.shao@gmail.com> <3315D21B-0772-4312-BCFB-402F408B0EF6@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 3FE92C000D X-Stat-Signature: 4mwnx1qj55adoyjoggmrwfnqnwzwdcw8 X-Rspam-User: X-HE-Tag: 1744184109-514917 X-HE-Meta: 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 GDCbUUJS jzqNo7hutXXagYO/Zy4qb3zM3I1beJ11AO9E3f3Jm3oIhUNQwb9Dw/kJEZDXieTCuSN3e1Z6PhK3jtjrM8LaumlN38LEhAz6lEovoSZxzj9qulu5AkJEN+bVttGJuVkbuSYZP4U4JID3TmudY0+n64MuJcqDmRZ2B5lGJjHqomUC+WSHk3wa9W3XF7I+pPJzw2HMwoKPXgb/OhkaSztntf+QbtbUrxlGXaj9+0WUDFPH6hxzacoZ6dFH577G4LMXcxH/EKzNVZJ5eEjPVVBmWnQV9c6h9obTzE8vPLTcaZRnfZ4dhecfkbH4b4aI4FaA/001B4Bhb6se/9SBqe1D+xOSY4kyYF4Fd00PoDf6ma7OQ6mW7VAHp5UGP0a242quJF66zJmtTNx0cMPSXNy/arOR4sCPSCLB8wyC7p3LnpgI6QzkWtJVXhXQLqEB9wfs3pL82tMlh+W32Kx0K0rckHeqYsA== 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 Thu 03-04-25 21:51:46, Michal Hocko wrote: > Add Andrew Andrew, do you want me to repost the patch or can you take it from this email thread? > Also, Dave do you want me to redirect xlog_cil_kvmalloc to kvmalloc or > do you preffer to do that yourself? > > On Thu 03-04-25 09:43:41, Michal Hocko wrote: > > There are users like xfs which need larger allocations with NOFAIL > > sementic. They are not using kvmalloc currently because the current > > implementation tries too hard to allocate through the kmalloc path > > which causes a lot of direct reclaim and compaction and that hurts > > performance a lot (see 8dc9384b7d75 ("xfs: reduce kvmalloc overhead for > > CIL shadow buffers") for more details). > > > > kvmalloc does support __GFP_RETRY_MAYFAIL semantic to express that > > kmalloc (physically contiguous) allocation is preferred and we should go > > more aggressive to make it happen. There is currently no way to express > > that kmalloc should be very lightweight and as it has been argued [1] > > this mode should be default to support kvmalloc(NOFAIL) with a > > lightweight kmalloc path which is currently impossible to express as > > __GFP_NOFAIL cannot be combined by any other reclaim modifiers. > > > > This patch makes all kmalloc allocations GFP_NOWAIT unless > > __GFP_RETRY_MAYFAIL is provided to kvmalloc. This allows to support both > > fail fast and retry hard on physically contiguous memory with vmalloc > > fallback. > > > > There is a potential downside that relatively small allocations (smaller > > than PAGE_ALLOC_COSTLY_ORDER) could fallback to vmalloc too easily and > > cause page block fragmentation. We cannot really rule that out but it > > seems that xlog_cil_kvmalloc use doesn't indicate this to be happening. > > > > [1] https://lore.kernel.org/all/Z-3i1wATGh6vI8x8@dread.disaster.area/T/#u > > Signed-off-by: Michal Hocko > > --- > > mm/slub.c | 8 +++++--- > > 1 file changed, 5 insertions(+), 3 deletions(-) > > > > diff --git a/mm/slub.c b/mm/slub.c > > index b46f87662e71..2da40c2f6478 100644 > > --- a/mm/slub.c > > +++ b/mm/slub.c > > @@ -4972,14 +4972,16 @@ static gfp_t kmalloc_gfp_adjust(gfp_t flags, size_t size) > > * We want to attempt a large physically contiguous block first because > > * it is less likely to fragment multiple larger blocks and therefore > > * contribute to a long term fragmentation less than vmalloc fallback. > > - * However make sure that larger requests are not too disruptive - no > > - * OOM killer and no allocation failure warnings as we have a fallback. > > + * However make sure that larger requests are not too disruptive - i.e. > > + * do not direct reclaim unless physically continuous memory is preferred > > + * (__GFP_RETRY_MAYFAIL mode). We still kick in kswapd/kcompactd to start > > + * working in the background but the allocation itself. > > */ > > if (size > PAGE_SIZE) { > > flags |= __GFP_NOWARN; > > > > if (!(flags & __GFP_RETRY_MAYFAIL)) > > - flags |= __GFP_NORETRY; > > + flags &= ~__GFP_DIRECT_RECLAIM; > > > > /* nofail semantic is implemented by the vmalloc fallback */ > > flags &= ~__GFP_NOFAIL; > > -- > > 2.49.0 > > > > -- > Michal Hocko > SUSE Labs -- Michal Hocko SUSE Labs