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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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Spam-Level: X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_TLS_ALL(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; RCPT_COUNT_TWELVE(0.00)[12]; MISSING_XM_UA(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[suse.cz,vger.kernel.org,kvack.org,lists.ozlabs.org,linux-foundation.org,nvidia.com,ellerman.id.au,gmail.com,csgroup.eu,kernel.org,linux.ibm.com]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; FUZZY_BLOCKED(0.00)[rspamd.com]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo] X-Spam-Score: -4.30 X-Spam-Flag: NO 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