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Tue, 2 Jun 2026 13:46:59 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id YJ3xAdPeHmraSwAAD6G6ig (envelope-from ); Tue, 02 Jun 2026 13:46:59 +0000 Date: Tue, 2 Jun 2026 14:46:57 +0100 From: Pedro Falcato To: Dennis Zhou Cc: Kaitao Cheng , akpm@linux-foundation.org, tj@kernel.org, cl@gentwo.org, mhocko@suse.com, vbabka@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, muchun.song@linux.dev, Kaitao Cheng Subject: Re: [PATCH 1/2] mm/percpu: Preserve NOFS/NOIO scope during chunk create and populate Message-ID: References: <20260528132917.81123-1-kaitao.cheng@linux.dev> <20260528132917.81123-2-kaitao.cheng@linux.dev> <5a4aa532-77a0-436a-8f5e-1bbcf2db6bbb@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Action: no action X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 72E4720003 X-Stat-Signature: zuxnk3wwin16mun78qscberq1zarz8c8 X-HE-Tag: 1780408022-42309 X-HE-Meta: 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 czrpsdzz IF9rlJoMTAFaq3n/8QvEyPBQkg+HimOSpZISukDjsfQGZ0Udz1k16liC8UDqjXRHR1IcQDbtfDKtshpF88k1Zs6K9mZTWDuqvpoz+2Vucnch5R8gjyhWgGtSqif7FPbhQsmjqt5MmaI390vE/HNfFe2I6dbf0YH8Mu4U5MNeJKvSfYuDgYajfB7mCupQCD3JXYyei1eM7fdG7uQQuDh1Ar0KVIzXLYWwFdEnvo+4FHdtln5VVVD4AtvQYRKLszvdG4MUodbA4nZXpEOzA8deNdJwi6hVl1L8Qk0uvXhLRZ2qkuxtzJQTQ36Lhn2I6MxYGwf8X Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, May 30, 2026 at 03:32:19PM +0200, Dennis Zhou wrote: > > > > I’ll try to do it. > > > > Following your suggestion, including in [PATCH 2/2], I will also try a > > different approach and fix the issue by reducing the scope of the > > pcpu_alloc_mutex critical section. > > > > No please don't. The point of the percpu mutex is to ensure that only > one person is ever possibly creating a new chunk. If you drop the mutex, > then you have to deal with concurrent callers when available percpu > memory is low. Percpu memory is expensive and unmovable so the cost is > in the control plane to avoid excess fragmentation. And so is slab memory, yet this is not a problem. We shouldn't keep problematic locks just because they may aid fragmentation slightly. -- Pedro