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Wed, 17 Dec 2025 11:12:48 +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 SQVrKTCQQmmxUgAAD6G6ig (envelope-from ); Wed, 17 Dec 2025 11:12:48 +0000 Message-ID: <1cf7675a-2de3-425f-9938-af97f7c6436d@suse.cz> Date: Wed, 17 Dec 2025 12:12:48 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/page_alloc: restore 0-handling to zone_set_pageset_high_and_batch Content-Language: en-US To: Joshua Hahn , Andrew Morton Cc: Daniel Palmer , Guenter Roeck , Brendan Jackman , Johannes Weiner , Michal Hocko , Suren Baghdasaryan , Zi Yan , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Matthew Wilcox References: <20251217060505.681923-1-joshua.hahnjy@gmail.com> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJnyBr8BQka0IFQAAoJECJPp+fMgqZkqmMQ AIbGN95ptUMUvo6aAdhxaOCHXp1DfIBuIOK/zpx8ylY4pOwu3GRe4dQ8u4XS9gaZ96Gj4bC+ jwWcSmn+TjtKW3rH1dRKopvC07tSJIGGVyw7ieV/5cbFffA8NL0ILowzVg8w1ipnz1VTkWDr 2zcfslxJsJ6vhXw5/npcY0ldeC1E8f6UUoa4eyoskd70vO0wOAoGd02ZkJoox3F5ODM0kjHu Y97VLOa3GG66lh+ZEelVZEujHfKceCw9G3PMvEzyLFbXvSOigZQMdKzQ8D/OChwqig8wFBmV QCPS4yDdmZP3oeDHRjJ9jvMUKoYODiNKsl2F+xXwyRM2qoKRqFlhCn4usVd1+wmv9iLV8nPs 2Db1ZIa49fJet3Sk3PN4bV1rAPuWvtbuTBN39Q/6MgkLTYHb84HyFKw14Rqe5YorrBLbF3rl M51Dpf6Egu1yTJDHCTEwePWug4XI11FT8lK0LNnHNpbhTCYRjX73iWOnFraJNcURld1jL1nV r/LRD+/e2gNtSTPK0Qkon6HcOBZnxRoqtazTU6YQRmGlT0v+rukj/cn5sToYibWLn+RoV1CE Qj6tApOiHBkpEsCzHGu+iDQ1WT0Idtdynst738f/uCeCMkdRu4WMZjteQaqvARFwCy3P/jpK uvzMtves5HvZw33ZwOtMCgbpce00DaET4y/UzsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZ8gcVAUJFhTonwAKCRAiT6fnzIKmZLY8D/9uo3Ut9yi2YCuASWxr7QQZ lJCViArjymbxYB5NdOeC50/0gnhK4pgdHlE2MdwF6o34x7TPFGpjNFvycZqccSQPJ/gibwNA zx3q9vJT4Vw+YbiyS53iSBLXMweeVV1Jd9IjAoL+EqB0cbxoFXvnjkvP1foiiF5r73jCd4PR rD+GoX5BZ7AZmFYmuJYBm28STM2NA6LhT0X+2su16f/HtummENKcMwom0hNu3MBNPUOrujtW khQrWcJNAAsy4yMoJ2Lw51T/5X5Hc7jQ9da9fyqu+phqlVtn70qpPvgWy4HRhr25fCAEXZDp xG4RNmTm+pqorHOqhBkI7wA7P/nyPo7ZEc3L+ZkQ37u0nlOyrjbNUniPGxPxv1imVq8IyycG AN5FaFxtiELK22gvudghLJaDiRBhn8/AhXc642/Z/yIpizE2xG4KU4AXzb6C+o7LX/WmmsWP Ly6jamSg6tvrdo4/e87lUedEqCtrp2o1xpn5zongf6cQkaLZKQcBQnPmgHO5OG8+50u88D9I rywqgzTUhHFKKF6/9L/lYtrNcHU8Z6Y4Ju/MLUiNYkmtrGIMnkjKCiRqlRrZE/v5YFHbayRD dJKXobXTtCBYpLJM4ZYRpGZXne/FAtWNe4KbNJJqxMvrTOrnIatPj8NhBVI0RSJRsbilh6TE m6M14QORSWTLRg== In-Reply-To: <20251217060505.681923-1-joshua.hahnjy@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: hpa6uouuu6jtatnhhq8pjxx1kjs46ow7 X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 96218A000F X-HE-Tag: 1765969971-82707 X-HE-Meta: U2FsdGVkX18PEe0+otwkrnx7pe0J7XYOFDPXPVFo49RDcItCFGW7bzAOQNC0i20QIMbVxUzKZrrJxrLOrl2vFbbv3rZ7fxAU2u26n3vS/vzOlEAaFiIiGKHMshBbYP4oNaY/U7czhBLKbwuu0nl2hyP0AbGolRFK7FsYsD84BUMIYFMT/HTgKTwvYJWgRqeZTvfldI5qryft9XoNXcESWPzoicx9Yw/m5jGUt2rqQdRi4433uOy09oE58bBZ2RR8qyqgnBFivz3wQrb/8aV8LP5RRw+ySdn2jOrJzMybLgKPhjYM+LjUlRdmaki7oYnPQoKF+39XCkqtc1o+bUYl1/42ZMb58vSV5X5JOawvU+ZC99P2fAdwX4di6JB+4Y9v9NiZ9f5GGh1YTWB0yxlI6Bf3N9grve/ug3TfYV+bS96VaPwXDrz4lZgV7mLkliFfChXcC314IiHzxtAT4Ry1WS0Qz1X/VL1yeBHhmVuVmC9M5gWQOy/XwtZ2iwzMmqUyxkyTZo5iKzNJrjXNf3z3XN4hbG1DzzjOSLsjiHWTJBHueidiV2wwR2YocI6Z3gO57wavnBxeVRRuzhJ9VOsRgSS3LYktRQYBCH6ns7csRDpXaW0TCh2yMbzU5sCmY5l56owe6Do0/T+DlY7kF/oTTJeZ/TM1w91c7rYC8/9BNvCrYcpyfSoZb3qDOD6ZMk5j0mIkKSgDoyw1HrTULfsKc5eG9wwQclfLHM6xPsCjDFuCFHAjBh87kLsvuGtzXdWg1uneckUooSTmq7xoZgq6/ZOVzP7Zz60iwlbTlmgoF3tMDjKyvVdMY2UP4MO0g9hgwri8iqehnWUiOATKvbxaR7j+Lkn+LOK25Z/QUAUeCyr6EnLTfK8rbPZ88nl1+8qnmjInvQmdWusF2tevrTctkljc+zMhqozR+cAkXH2maR697TsiO/aP69tiWANyGW4tb65ytQp460VEfxTkSfU rYhuMsNo 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 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 12/17/25 07:05, Joshua Hahn wrote: > Commit 2783088ef24e ("mm/page_alloc: prevent reporting pcp->batch = 0") > moved the error handling (0-handling) of zone_batchsize from its > callers to inside the function. However, the commit left out the error > handling for the NOMMU case, leading to deadlocks on NOMMU systems. > > Since in the NOMMU case the reported-to-user batchsize should still be 0, Should it? The value is effectively set to 1 despite what zone_batchsize() returns, because of that adjustment this patch reinstates. Also does anyone care, really? > we would only like the error handling to exist in the callsites that > set the internal value for the zone (i.e. zone_set_pageset_high_and_batch). > > Restore max(1, zone_batchsize(zone)) to the callsite to prevent errors > on NOMMU systems. I would rather make zone_batchsize() for !CONFIG_MMU return 1 instead of 0. > Fixes: 2783088ef24e ("mm/page_alloc: prevent reporting pcp->batch = 0") > Reported-by: Daniel Palmer > Closes: https://lore.kernel.org/linux-mm/CAFr9PX=_HaM3_xPtTiBn5Gw5-0xcRpawpJ02NStfdr0khF2k7g@mail.gmail.com/ > Reported-by: Guenter Roeck > Closes: https://lore.kernel.org/all/42143500-c380-41fe-815c-696c17241506@roeck-us.net/ > Signed-off-by: Joshua Hahn > --- > 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 822e05f1a964..10c1297fd3ea 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -6045,7 +6045,7 @@ static void zone_set_pageset_high_and_batch(struct zone *zone, int cpu_online) > { > int new_high_min, new_high_max, new_batch; > > - new_batch = zone_batchsize(zone); > + new_batch = max(1, zone_batchsize(zone)); > if (percpu_pagelist_high_fraction) { > new_high_min = zone_highsize(zone, new_batch, cpu_online, > percpu_pagelist_high_fraction); > > base-commit: 40fbbd64bba6c6e7a72885d2f59b6a3be9991eeb