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Fri, 1 Dec 2023 09:33:02 +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 XBWZIU6oaWWRUQAAD6G6ig (envelope-from ); Fri, 01 Dec 2023 09:33:02 +0000 Date: Fri, 1 Dec 2023 10:33:01 +0100 From: Michal Hocko To: Johannes Weiner Cc: Dan Schatzberg , Roman Gushchin , Yosry Ahmed , Huan Yang , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, Shakeel Butt , Muchun Song , Andrew Morton , David Hildenbrand , Matthew Wilcox , Huang Ying , Kefeng Wang , Peter Xu , "Vishal Moola (Oracle)" , Yue Zhao , Hugh Dickins Subject: Re: [PATCH 0/1] Add swappiness argument to memory.reclaim Message-ID: References: <20231130153658.527556-1-schatzberg.dan@gmail.com> <20231130165642.GA386439@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231130165642.GA386439@cmpxchg.org> X-Spamd-Bar: +++++++++++++++ X-Spam: Yes X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 8870440006 X-Stat-Signature: hrypo7h8nufxshxpxymra5xmf7qudhym X-HE-Tag: 1701423185-877406 X-HE-Meta: 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 7gvFwxkS jfqVkMDPoUjn+8McSFAwgSt6xKzknXKSA4bcG7a27lh/kS1qoo5uQaRWfHnKGUsXTJC823QwffjLcuE5pnS544MxwLD7digH7PTkovaAWp6mslN07fNU8DXwOTchFkh4aTNhM2zj/0+jJi90tlMhoGgKAbDp9vcrjPlvvIi6d2XbXPvDPu/OzPMb7Ns3ufpnV/rcVnlKGDcSprqWGhNvEeYSxRWa6ZFYZIZY19JBpHiEiLLlPIoMZ8LDKAA== 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 30-11-23 11:56:42, Johannes Weiner wrote: [...] > So I wouldn't say it's merely a reclaim hint. It controls a very > concrete and influential factor in VM decision making. And since the > global swappiness is long-established ABI, I don't expect its meaning > to change significantly any time soon. As I've said I am more worried about potential future changes which would modify existing, reduce or add more corner cases which would be seen as a change of behavior from the user space POV. That means that we would have to be really explicit about the fact that the reclaim is free to override the swappiness provided by user. So essentially a best effort interface without any actual guarantees. That surely makes it harder to use. Is it still useable? Btw. IIRC these concerns were part of the reason why memcg v2 doesn't have swappiness interface. If we decide to export swappiness via memory.reclaim interface does it mean we will do so on per-memcg level as well? -- Michal Hocko SUSE Labs