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Wed, 4 Dec 2024 09:15:24 +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 wN0nEawdUGfYaAAAD6G6ig (envelope-from ); Wed, 04 Dec 2024 09:15:24 +0000 Date: Wed, 4 Dec 2024 10:15:14 +0100 From: Oscar Salvador To: Vlastimil Babka Cc: David Hildenbrand , 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> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <15096b27-6f27-45fc-8a8b-de781a9c42a5@suse.cz> X-Rspamd-Pre-Result: action=no action; module=replies; Message is reply to one we originated X-Spamd-Result: default: False [-4.00 / 50.00]; REPLY(-4.00)[]; ASN(0.00)[asn:25478, ipnet:::/0, country:RU] X-Rspamd-Queue-Id: F26A72115C X-Rspamd-Pre-Result: action=no action; module=replies; Message is reply to one we originated X-Rspamd-Action: no action X-Rspamd-Server: rspamd1.dmz-prg2.suse.org 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. -- Oscar Salvador SUSE Labs