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Wed, 4 Dec 2024 08:54:54 +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 gfnvNN4YUGf8YQAAD6G6ig (envelope-from ); Wed, 04 Dec 2024 08:54:54 +0000 Message-ID: Date: Wed, 4 Dec 2024 09:54:54 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RESEND v2 4/6] mm/page_alloc: sort out the alloc_contig_range() gfp flags mess To: David Hildenbrand , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, Andrew Morton , Oscar Salvador , Zi Yan , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Naveen N Rao , Madhavan Srinivasan 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> Content-Language: en-US From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Pre-Result: action=no action; module=replies; Message is reply to one we originated X-Spam-Level: X-Spamd-Result: default: False [-4.00 / 50.00]; REPLY(-4.00)[]; ASN(0.00)[asn:25478, ipnet:::/0, country:RU] X-Spam-Score: -4.00 X-Spam-Flag: NO X-Rspamd-Queue-Id: 0212021158 X-Rspamd-Pre-Result: action=no action; module=replies; Message is reply to one we originated X-Rspamd-Action: no action X-Rspamd-Server: rspamd2.dmz-prg2.suse.org On 12/3/24 20:19, David Hildenbrand wrote: > On 03.12.24 15:24, Vlastimil Babka wrote: >> On 12/3/24 15:12, David Hildenbrand wrote: >>> On 03.12.24 14:55, Vlastimil Babka wrote: >>> likely the thing we are assuming here is that we are migrating a page, and >>> usually, these are user allocation (except maybe balloon and some other non-lru >>> movable things). >> >> Yeah and user allocations obey cpuset and mempolicies etc. But these are >> likely somebody elses allocations that were done according to their >> policies. With our migration we might be actually violating those, which >> probably can't be helped (is at least migration within the same node >> preferred? hmm). > > I would hope that we handle memory policies somehow (via VMAs? not > sure). cpuset? I have no idea. They are handled when allocating, but then the info is lost, the allocation doesn't carry its effective nodemask. But that's really a separate issue that just occured to me. > But it doesn't seem to me that our caller's restrictions >> (if those exist, would be enforced by __GFP_HARDWALL) are that relevant for >> somebody else's pages? > > 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. Yeah I agree a refactoring patch shouldn't change the existing behavior... > 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. > > I can look into it + send a follow-up patch. ...but it's a great opportunity to start questioning it and possibly change it as a follow up :) Thanks! > Thanks! >