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bh=z7GKbEJp2q0NJZLK9xT8xoBwCMAwop0nDLxGQi+CYvs=; b=g93LYDPCILhrhfTopoUnYlnAwa/Q9q8sGWT4FL40wUX2bePTUmpfwhInx3/CFIbGU2WYIH ktD7hMrSFz5h32Dg== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 9F27C13A3E; Fri, 29 Aug 2025 08:38:24 +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 NdA6JQBnsWjmIAAAD6G6ig (envelope-from ); Fri, 29 Aug 2025 08:38:24 +0000 Message-ID: <77058118-b481-4c45-8f86-d9a67ea6a187@suse.cz> Date: Fri, 29 Aug 2025 10:38:24 +0200 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] mm/page_alloc: only set ALLOC_HIGHATOMIC for __GPF_HIGH allocations Content-Language: en-US From: Vlastimil Babka To: Thadeu Lima de Souza Cascardo , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Andrew Morton , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Mel Gorman , kernel-dev@igalia.com, Helen Koike , Matthew Wilcox , Thierry Reding , Sergey Senozhatsky , neil@brown.name References: <20250814172245.1259625-1-cascardo@igalia.com> <10cdada2-f28f-4868-b821-4a13ed627e76@suse.cz> Autocrypt: addr=vbabka@suse.cz; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spamd-Result: default: False [-3.01 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCPT_COUNT_TWELVE(0.00)[16]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; FREEMAIL_CC(0.00)[kvack.org,linux-foundation.org,google.com,suse.com,cmpxchg.org,nvidia.com,techsingularity.net,igalia.com,infradead.org,gmail.com,chromium.org,brown.name]; RCVD_TLS_ALL(0.00)[]; DKIM_TRACE(0.00)[suse.cz:+]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; DNSWL_BLOCKED(0.00)[2a07:de40:b281:106:10:150:64:167:received,2a07:de40:b281:104:10:150:64:97:from]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; TAGGED_RCPT(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email,suse.com:email,suse.cz:mid,suse.cz:dkim,suse.cz:email,imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns] X-Spam-Flag: NO X-Spam-Level: X-Rspamd-Queue-Id: C7BF420544 X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Rspamd-Action: no action X-Spam-Score: -3.01 On 8/29/25 10:36, Vlastimil Babka wrote: > On 8/14/25 19:22, Thadeu Lima de Souza Cascardo wrote: >> Commit 524c48072e56 ("mm/page_alloc: rename ALLOC_HIGH to >> ALLOC_MIN_RESERVE") is the start of a series that explains how __GFP_HIGH, >> which implies ALLOC_MIN_RESERVE, is going to be used instead of >> __GFP_ATOMIC for high atomic reserves. >> >> Commit eb2e2b425c69 ("mm/page_alloc: explicitly record high-order atomic >> allocations in alloc_flags") introduced ALLOC_HIGHATOMIC for such >> allocations of order higher than 0. It still used __GFP_ATOMIC, though. >> >> Then, commit 1ebbb21811b7 ("mm/page_alloc: explicitly define how __GFP_HIGH >> non-blocking allocations accesses reserves") just turned that check for >> !__GFP_DIRECT_RECLAIM, ignoring that high atomic reserves were expected to >> test for __GFP_HIGH. >> >> This leads to high atomic reserves being added for high-order GFP_NOWAIT >> allocations and others that clear __GFP_DIRECT_RECLAIM, which is >> unexpected. Later, those reserves lead to 0-order allocations going to the >> slow path and starting reclaim. >> >> From /proc/pagetypeinfo, without the patch: >> >> Node 0, zone DMA, type HighAtomic 0 0 0 0 0 0 0 0 0 0 0 >> Node 0, zone DMA32, type HighAtomic 1 8 10 9 7 3 0 0 0 0 0 >> Node 0, zone Normal, type HighAtomic 64 20 12 5 0 0 0 0 0 0 0 >> >> With the patch: >> >> Node 0, zone DMA, type HighAtomic 0 0 0 0 0 0 0 0 0 0 0 >> Node 0, zone DMA32, type HighAtomic 0 0 0 0 0 0 0 0 0 0 0 >> Node 0, zone Normal, type HighAtomic 0 0 0 0 0 0 0 0 0 0 0 >> >> Fixes: 1ebbb21811b7 ("mm/page_alloc: explicitly define how __GFP_HIGH non-blocking allocations accesses reserves") >> Signed-off-by: Thadeu Lima de Souza Cascardo >> Tested-by: Helen Koike >> Cc: Mel Gorman >> Cc: Michal Hocko >> Cc: Matthew Wilcox >> Cc: NeilBrown >> Cc: Thierry Reding >> Cc: Vlastimil Babka > > Agreed with others that this change matches the original intention and it > must have been an oversight. Also found nothing to the contrary in the > original threads. Oops, forgot to add Reviewed-by: Vlastimil Babka >> --- >> mm/page_alloc.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index 2ef3c07266b3..bf52e3bef626 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -4219,7 +4219,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask, unsigned int order) >> if (!(gfp_mask & __GFP_NOMEMALLOC)) { >> alloc_flags |= ALLOC_NON_BLOCK; >> >> - if (order > 0) >> + if (order > 0 && (alloc_flags & ALLOC_MIN_RESERVE)) >> alloc_flags |= ALLOC_HIGHATOMIC; >> } >> >