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b=BrE+ZMtfse74Rx9gXb8TBDlul9CFpphp+iDqcuvaKvn+la0P4nw5x+dpLJxpxymss Fs3KqhtyP8Y5icHlBfXtie/e7n3oDDCiUPhZMb2z4zlcBvtOi8L+OmAJuavGfAlGrs cXtecutkELrLQLHpstHEKDgODcyKR1f9W8IYLMCJ5IN1eY5iumCefMXOEHCTqsuitP ny3AZ/M7WoDBugBXgLtjoiKCabNy4omvWzIwPrvn8EX3kpo73VlkRer+YmR0M1jHGH kROjVJDipV2iUMvn9dIfWNAesAHo6z6phJRoseA1bL5GIfnFKW3k4F/FOU9ZFkNNN+ E/dfVEFGq0SAg== Message-ID: <8cc503d9-04a1-4d90-874c-ada6c0ac5147@kernel.org> Date: Fri, 4 Sep 2026 16:11:57 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4] mm/page_alloc: avoid direct compaction for costly __GFP_NORETRY allocations Content-Language: en-US To: Salvatore Dipietro , linux-kernel@vger.kernel.org, hch@infradead.org Cc: abuehaze@amazon.com, akpm@linux-foundation.org, alisaidi@amazon.com, blakgeof@amazon.com, brauner@kernel.org, dgc@kernel.org, dipietro.salvatore@gmail.com, djwong@kernel.org, hannes@cmpxchg.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-xfs@vger.kernel.org, mhocko@suse.com, ritesh.list@gmail.com, rvvandan@amazon.com, stable@vger.kernel.org, surenb@google.com, willy@infradead.org, ziy@nvidia.com, David Hildenbrand , Christoph Hellwig , Brendan Jackman References: <20260904115629.3993331-1-dipiets@amazon.it> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: D7E7C20009 X-Stat-Signature: 56amncsx3hnfz33p5f7qjdman7b73rea X-HE-Tag: 1788531124-127823 X-HE-Meta: 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 +5VxerPd 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/4/26 13:56, Salvatore Dipietro wrote: > Commit 5d8edfb900d5 ("iomap: Copy larger chunks from userspace") > introduced high-order folio allocations in the iomap buffered write > path. When memory is fragmented, each failed costly-order allocation > enters __alloc_pages_slowpath() which runs direct compaction and > drain_all_pages(), causing a 0.38x throughput drop on PostgreSQL > pgbench (simple-update) with 1024 clients on a 96-vCPU arm64 system. > > The root issue is that direct compaction is too expensive for hot > allocation paths that have fallbacks to smaller allocations. > __filemap_get_folio_mpol() already marks higher-order allocations with > __GFP_NORETRY | __GFP_NOWARN, signalling that the caller can handle > failure. However, the page allocator still attempts full direct > compaction for costly orders with __GFP_NORETRY, which is unnecessarily > aggressive when the caller will simply retry at a lower order. > > For costly-order allocations with __GFP_NORETRY, clear > __GFP_DIRECT_RECLAIM at the very start of the slowpath, before > can_direct_reclaim, can_compact and the nofail checks are evaluated. > This makes the entire slowpath treat the request as non-blocking: no > direct reclaim, no direct compaction and no drain_all_pages() IPI > across every CPU. kswapd (and in turn kcompactd) is still woken further > down for background defragmentation, so compaction keeps working for > long-term system health while being removed from the latency-critical > direct allocation path. > > Allocations that also request __GFP_THISNODE are exempted. That flag > pairing identifies the local-node-first THP attempt issued by > alloc_pages_mpol() (mempolicy.c), which relies on direct compaction to > form transparent huge pages. > > Test environment: > Hardware: AWS EC2 m8g.24xlarge (96 vCPU, arm64) > 12x 1TB IO2 32000 IOPS RAID0 XFS > OS: AL2023 > Kernel: v7.3-rc1 > Database: PostgreSQL 18.4 > Workload: pgbench simple-update, 1024 clients, 96 threads, 1200s > > Results (average of 3 runs, TPS): > > Config Avg TPS % vs Baseline > baseline (no patch) 59,408 - > With this patch 155,409 +161.6% > > Link: https://lore.kernel.org/all/20260403193535.9970-1-dipiets@amazon.it/T/#t [v1] > Link: https://lore.kernel.org/linux-mm/20260420161404.642-1-dipiets@amazon.it/T/#u [v2] > Link: https://lore.kernel.org/all/20260710143437.12379-1-dipiets@amazon.it/T/#u [v3] > Fixes: 5d8edfb900d5 ("iomap: Copy larger chunks from userspace") > Cc: stable@vger.kernel.org > Cc: Andrew Morton > Cc: Vlastimil Babka > Cc: David Hildenbrand > Cc: Michal Hocko > Cc: Johannes Weiner > Cc: Matthew Wilcox > Cc: Christoph Hellwig > Cc: Dave Chinner > Cc: Ritesh Harjani > Cc: linux-mm@kvack.org > Cc: linux-fsdevel@vger.kernel.org > Cc: linux-xfs@vger.kernel.org > Signed-off-by: Salvatore Dipietro I guess this will have to do until unlikely(we figure out a better API)... Acked-by: Vlastimil Babka (SUSE) > --- > v4: Clear __GFP_DIRECT_RECLAIM early in the slowpath and exempt > __GFP_THISNODE so THP attempt keeps using direct compaction > v3: Move to mm/page_alloc.c, wake kcompactd instead of avoiding it > v2: Move from fs/iomap/buffered-io.c to mm/filemap.c > v1: Avoid compaction in iomap folio allocation > > mm/page_alloc.c | 18 +++++++++++++++--- > 1 file changed, 15 insertions(+), 3 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 12fac9084c48..542c2ec31061 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4784,10 +4784,10 @@ static inline struct page * > __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > struct alloc_context *ac) > { > - bool can_direct_reclaim = gfp_mask & __GFP_DIRECT_RECLAIM; > - bool can_compact = can_direct_reclaim && gfp_compaction_allowed(gfp_mask); > - bool nofail = gfp_mask & __GFP_NOFAIL; > const bool costly_order = order > PAGE_ALLOC_COSTLY_ORDER; > + bool can_direct_reclaim; > + bool can_compact; > + bool nofail; > struct page *page = NULL; > unsigned int alloc_flags; > unsigned long did_some_progress; > @@ -4802,6 +4802,18 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > bool can_retry_reserves = true; > unsigned long alloc_start_time = jiffies; > > + /* > + * Costly __GFP_NORETRY callers have a cheap fallback, so don't stall > + * them in reclaim or compaction. __GFP_THISNODE callers are exempt. > + */ > + if (costly_order && (gfp_mask & __GFP_NORETRY) && > + !(gfp_mask & __GFP_THISNODE)) > + gfp_mask &= ~__GFP_DIRECT_RECLAIM; > + > + can_direct_reclaim = gfp_mask & __GFP_DIRECT_RECLAIM; > + can_compact = can_direct_reclaim && gfp_compaction_allowed(gfp_mask); > + nofail = gfp_mask & __GFP_NOFAIL; > + > if (unlikely(nofail)) { > /* > * Also we don't support __GFP_NOFAIL without __GFP_DIRECT_RECLAIM,