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Mon, 24 Jun 2024 08:16:00 +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 gPxPLkAreWbGDQAAD6G6ig (envelope-from ); Mon, 24 Jun 2024 08:16:00 +0000 Received: by quack3.suse.cz (Postfix, from userid 1000) id 5CC5DA08A4; Mon, 24 Jun 2024 10:16:00 +0200 (CEST) Date: Mon, 24 Jun 2024 10:16:00 +0200 From: Jan Kara To: Andrew Morton Cc: Jan Kara , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Zach O'Keefe Subject: Re: [PATCH 2/2] mm: Avoid overflows in dirty throttling logic Message-ID: <20240624081600.fi4om7huw3w5oxy4@quack3> References: <20240621144017.30993-1-jack@suse.cz> <20240621144246.11148-2-jack@suse.cz> <20240621101058.afff9eb37e99fd48452599b7@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240621101058.afff9eb37e99fd48452599b7@linux-foundation.org> X-Rspamd-Action: no action X-Rspamd-Queue-Id: D5483C0002 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: i1kgwk6ucpbkws9xwkd61o7c5yq5kubd X-HE-Tag: 1719216962-645022 X-HE-Meta: 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 1nn9cHNZ 4s7GiGW3HwKAZY+KSmTp5aXEEmhAj4E3ErmRYEL4HP64HG/riBXsUlrHsCowxGl8ZynuCKjMHV+EE3lSkRoNAPQpkmRdZ0DZRZODocFlwP3vzIIZeNy5Gho35UyFbOSKBw0FKFbnefesORhjTu9J/6tZhICMyZL6+vL1whPJDb3fRP+XE/V2n7PKIEwK1yHLG6RmEP91Ygm5GW495HyF5T3dkgzevV/FTAj8NH7CvAevGOgnREUEHQDglI4NAXbywEpke7oEtT8wVr9AfnxJ6zRkKizWrFxgL4FHqAypssSPJ/upH3oWJX38cDg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000002, 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 Fri 21-06-24 10:10:58, Andrew Morton wrote: > On Fri, 21 Jun 2024 16:42:38 +0200 Jan Kara wrote: > > > The dirty throttling logic is interspersed with assumptions that dirty > > limits in PAGE_SIZE units fit into 32-bit (so that various > > multiplications fit into 64-bits). If limits end up being larger, we > > will hit overflows, possible divisions by 0 etc. Fix these problems by > > never allowing so large dirty limits as they have dubious practical > > value anyway. For dirty_bytes / dirty_background_bytes interfaces we can > > just refuse to set so large limits. For dirty_ratio / > > dirty_background_ratio it isn't so simple as the dirty limit is computed > > from the amount of available memory which can change due to memory > > hotplug etc. So when converting dirty limits from ratios to numbers of > > pages, we just don't allow the result to exceed UINT_MAX. > > Shouldn't this also be cc:stable? So this is root-only triggerable problem and kind of "don't do it when it hurts" issue (who really wants to set dirty limits to > 16 TB?). So I'm not sure CC stable is warranted but I won't object. Honza -- Jan Kara SUSE Labs, CR