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b=HyIzudcHgwOZMnwvnVThzTbiSoYQgWKiZ7BSA5Nn93yO5ZwK9lei72TD5EsIyvErW IBdApPWF/AFiQzqCq6bhBEkYP7OBWar0qnqBy6tDn0UVNS/UQDyr4Tr49g9ife1kGG PjgiL6sCmL5DZQR2/qRy3V6BSx7RPXHJ9QG9Tsm6etiWSMv+PcWkqBXCseFJR0wKjC 2EiLaTBxgsBcsTcEPY6IrLBGKcD5HpS4iTaK+Ep2QcVcZ/xQT6/7WZKjkyW0RbAhX4 2QTChyiE4YyE/kBFyhpYK/tppcL5nZQpL7EuRWN9qfuuxq3FtATsfFiTdrsAKf0uIE phOj7bGLdPLfQ== Message-ID: <7ddb704c-76a9-4071-8969-06fa1403eb07@kernel.org> Date: Wed, 22 Jul 2026 14:35:51 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/page_alloc: avoid direct compaction for costly __GFP_NORETRY allocations Content-Language: en-US To: Salvatore Dipietro , hannes@cmpxchg.org, willy@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, hch@infradead.org, jackmanb@google.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-xfs@vger.kernel.org, mhocko@suse.com, ritesh.list@gmail.com, stable@vger.kernel.org, surenb@google.com, ziy@nvidia.com References: <20260714120204.542300-1-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: rspam03 X-Rspamd-Queue-Id: 3E1BE20009 X-Stat-Signature: dsbjgbequ8jfyewb7fuf11uykq6rgzra X-HE-Tag: 1784723758-20475 X-HE-Meta: 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 RnygqHog uAhJ/BRJlspVPUcVCe6vDx6NCtukjfucHxX6j/CeXaZz53mNryynhorlnBi1V1q3Xn7oUMyvTTctWPSrdbjn8K5phX0RHvcp5nmYqVKH41SDaSYHZTghobw9iccWmujemQh/jgGhkxyb8r+ONZ4sNeewZMLKqritg8J/0bkA9wdQX2K/jy1JYiRf8x+wT+W7bhdcYb2ZlXoKhDwcWdCIH020HfZvXbMGE4KcreKl/mmDkCtROS5VZrcU0XfrE6LcvxAGBqF48T1gUXZarcnSVanvkjrqtIk45XC2kU9tU0iITI80X9tmCslgIkHDxi1eLm29V283Yofpm2DNN079/metEH/l9XFjPpe4d1iOkzJrcbBmgrBR1wIzqglLLUYn1GBG5 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/14/26 14:02, Salvatore Dipietro wrote: > > Hi Johannes, Matthew, > > Thank you both for the alternative proposals. I've tested both > approaches on the same test environment used for v3. > > Results (4 runs each): > > Config Avg TPS % vs Baseline > -------------------------------------------------------- > baseline (no patch) 70,735 - > Johannes' approach 156,908 +121.8% > Matthew's approach 70,145 -0.8% (within noise) > > > Johannes' approach (clearing __GFP_DIRECT_RECLAIM early in the > slowpath for costly __GFP_NORETRY) delivers the same ~2.2x speedup > as v3, as expected - it prevents the entire direct reclaim and > compaction machinery from running for these opportunistic allocations. AFAICS both your v3 and the implemented Johannes' suggestion effectively make all the compact_first logic dead code - at least for the intended THP use case based on costly_order. It will only continue to do something for the non-movable order>0 case. So that's a significant change which will not show up in your results, but might affect other workloads (I'd expect mainly by having fewer THPs). > Matthew's filemap.c approach does not help in this workload. The > reason is that the first allocation attempt at max order still carries > __GFP_DIRECT_RECLAIM and enters the slowpath with direct compaction > enabled. The __GFP_DIRECT_RECLAIM clearing only takes effect for > subsequent lower-order attempts in the fallback loop, but the costly > compaction has already executed on the first try. > > Let me know if you have any other variant you want me to test, > or if I should prepare a v4 based on Johannes' suggestion. > > This is what I tested for Johannes' approach: > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index a63733dac659..6e960c969e67 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4733,10 +4733,10 @@ 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; > @@ -4751,6 +4751,20 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > bool can_retry_reserves = true; > unsigned long alloc_start_time = jiffies; > > + /* > + * Costly __GFP_NORETRY allocations are opportunistic: the caller > + * can fall back to smaller orders. Don't stall on direct reclaim > + * or compaction; clearing __GFP_DIRECT_RECLAIM makes the entire > + * slowpath treat this as a non-blocking request. kswapd will wake > + * kcompactd as needed for background defragmentation. > + */ > + if (costly_order && (gfp_mask & __GFP_NORETRY)) > + 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, > > > Thanks, > Salvatore > > > > > > AMAZON DEVELOPMENT CENTER ITALY SRL, viale Monte Grappa 3/5, 20124 Milano, Italia, Registro delle Imprese di Milano Monza Brianza Lodi REA n. 2504859, Capitale Sociale: 10.000 EUR i.v., Cod. Fisc. e P.IVA 10100050961, Societa con Socio Unico > > >