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Wed, 4 Dec 2024 10:04:30 +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 toxJBS4pUGfEdwAAD6G6ig (envelope-from ); Wed, 04 Dec 2024 10:04:30 +0000 Date: Wed, 4 Dec 2024 11:04:24 +0100 From: Oscar Salvador To: David Hildenbrand Cc: Vlastimil Babka , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, Andrew Morton , Zi Yan , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Naveen N Rao , Madhavan Srinivasan Subject: Re: [PATCH RESEND v2 4/6] mm/page_alloc: sort out the alloc_contig_range() gfp flags mess Message-ID: References: <20241203094732.200195-1-david@redhat.com> <20241203094732.200195-5-david@redhat.com> <96c92857-4850-4f85-9474-ac193c5ea48c@redhat.com> <04c1d28e-bbea-4499-9a6d-770f9ca53ba9@suse.cz> <15096b27-6f27-45fc-8a8b-de781a9c42a5@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: AB74F12000B X-Stat-Signature: oixpzxewjn469iuxuwdgt4gm3sbrc94t X-Rspam-User: X-HE-Tag: 1733306651-674665 X-HE-Meta: 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 Ghi9rYGz wYQs0i36/qh/AMnXQfEZCgtXW41Iy6KfL9E/riro5IiM0X/SUFgOYye080SOuyJD7uJbSq+woVXYNOkDb6nsXi8fNWtONjc20cAyS2Zhj1Hk9Yis2NWL13B1cNqUZYrIqla0WGWKjWDHCZ1o1/oPumd3EjSJE65aXLWDAWLAVaBuOEFnSKijVx0k8crtpNrf0+SQ9Wip0u48Gnu0Fy2t1JPtnyZYJAPmDkGqIKzjiw89OqsePpzD2NJmwPGESs0bKu+1d8DMh3cIz9/ZRbkTdqWsAdrQQrqha1+RVmXI/6Stull6Uvye5lWs13w== 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 Wed, Dec 04, 2024 at 10:28:39AM +0100, David Hildenbrand wrote: > On 04.12.24 10:15, Oscar Salvador wrote: > > On Wed, Dec 04, 2024 at 10:03:28AM +0100, Vlastimil Babka wrote: > > > On 12/4/24 09:59, Oscar Salvador wrote: > > > > On Tue, Dec 03, 2024 at 08:19:02PM +0100, David Hildenbrand wrote: > > > > > It was always set using "GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL", > > > > > and I removed the same flag combination in #2 from memory offline code, and > > > > > we do have the exact same thing in do_migrate_range() in > > > > > mm/memory_hotplug.c. > > > > > > > > > > We should investigate if__GFP_HARDWALL is the right thing to use here, and > > > > > if we can get rid of that by switching to GFP_KERNEL in all these places. > > > > > > > > Why would not we want __GFP_HARDWALL set? > > > > Without it, we could potentially migrate the page to a node which is not > > > > part of the cpuset of the task that originally allocated it, thus violating the > > > > policy? Is not that a problem? > > > > > > The task doing the alloc_contig_range() will likely not be the same task as > > > the one that originally allocated the page, so its policy would be > > > different, no? So even with __GFP_HARDWALL we might be already migrating > > > outside the original tasks's constraint? Am I missing something? > > > > Yes, that is right, I thought we derive the policy from the old page > > somehow when migrating it, but reading the code does not seem to be the > > case. > > > > Looking at prepare_alloc_pages(), if !ac->nodemask, which would be the > > case here, we would get the policy from the current task > > (alloc_contig_range()) when cpusets are enabled. > > > > So yes, I am a bit puzzled why __GFP_HARDWALL was chosen in the first > > place. > > I suspect because "GFP_USER" felt like the appropriate thing to do. Looking back at when the whole contiguous allocator patchset was posted, it seems that it kinda copied what memory-offline code was doing, which was migrating pages with GFP_HIGHUSER_MOVABLE (hotremove_migrate_alloc()). Then, the HIGHMEM modifier was dropped due to HIGHMEM restrictions on some systems, ending up with GFP_USER. -- Oscar Salvador SUSE Labs