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Tue, 25 Feb 2025 18:51:22 +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 NqGoAioRvmdYZQAAD6G6ig (envelope-from ); Tue, 25 Feb 2025 18:51:22 +0000 Message-ID: Date: Tue, 25 Feb 2025 19:51:21 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/page_alloc: Warn on nr_reserved_highatomic underflow Content-Language: en-US To: Brendan Jackman , Andrew Morton Cc: Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250225-warn-underflow-v1-1-3dc542941d3a@google.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+fMgqZkBQJkBREIBQkRadznAAoJECJPp+fMgqZkNxIQ ALZRqwdUGzqL2aeSavbum/VF/+td+nZfuH0xeWiO2w8mG0+nPd5j9ujYeHcUP1edE7uQrjOC Gs9sm8+W1xYnbClMJTsXiAV88D2btFUdU1mCXURAL9wWZ8Jsmz5ZH2V6AUszvNezsS/VIT87 AmTtj31TLDGwdxaZTSYLwAOOOtyqafOEq+gJB30RxTRE3h3G1zpO7OM9K6ysLdAlwAGYWgJJ V4JqGsQ/lyEtxxFpUCjb5Pztp7cQxhlkil0oBYHkudiG8j1U3DG8iC6rnB4yJaLphKx57NuQ PIY0Bccg+r9gIQ4XeSK2PQhdXdy3UWBr913ZQ9AI2usid3s5vabo4iBvpJNFLgUmxFnr73SJ KsRh/2OBsg1XXF/wRQGBO9vRuJUAbnaIVcmGOUogdBVS9Sun/Sy4GNA++KtFZK95U7J417/J Hub2xV6Ehc7UGW6fIvIQmzJ3zaTEfuriU1P8ayfddrAgZb25JnOW7L1zdYL8rXiezOyYZ8Fm ZyXjzWdO0RpxcUEp6GsJr11Bc4F3aae9OZtwtLL/jxc7y6pUugB00PodgnQ6CMcfR/HjXlae h2VS3zl9+tQWHu6s1R58t5BuMS2FNA58wU/IazImc/ZQA+slDBfhRDGYlExjg19UXWe/gMcl De3P1kxYPgZdGE2eZpRLIbt+rYnqQKy8UxlszsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZAUSmwUJDK5EZgAKCRAiT6fnzIKmZOJGEACOKABgo9wJXsbWhGWYO7mD 8R8mUyJHqbvaz+yTLnvRwfe/VwafFfDMx5GYVYzMY9TWpA8psFTKTUIIQmx2scYsRBUwm5VI EurRWKqENcDRjyo+ol59j0FViYysjQQeobXBDDE31t5SBg++veI6tXfpco/UiKEsDswL1WAr tEAZaruo7254TyH+gydURl2wJuzo/aZ7Y7PpqaODbYv727Dvm5eX64HCyyAH0s6sOCyGF5/p eIhrOn24oBf67KtdAN3H9JoFNUVTYJc1VJU3R1JtVdgwEdr+NEciEfYl0O19VpLE/PZxP4wX PWnhf5WjdoNI1Xec+RcJ5p/pSel0jnvBX8L2cmniYnmI883NhtGZsEWj++wyKiS4NranDFlA HdDM3b4lUth1pTtABKQ1YuTvehj7EfoWD3bv9kuGZGPrAeFNiHPdOT7DaXKeHpW9homgtBxj 8aX/UkSvEGJKUEbFL9cVa5tzyialGkSiZJNkWgeHe+jEcfRT6pJZOJidSCdzvJpbdJmm+eED w9XOLH1IIWh7RURU7G1iOfEfmImFeC3cbbS73LQEFGe1urxvIH5K/7vX+FkNcr9ujwWuPE9b 1C2o4i/yZPLXIVy387EjA6GZMqvQUFuSTs/GeBcv0NjIQi8867H3uLjz+mQy63fAitsDwLmR EP+ylKVEKb0Q2A== In-Reply-To: <20250225-warn-underflow-v1-1-3dc542941d3a@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: C35E1A0019 X-Stat-Signature: a344kc9jnwjro9naqd5t31qo9dppwy6o X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1740509483-582195 X-HE-Meta: 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 FYrgmEje bmKg6if1lP3YhWmLvLrHwxqWVCUVc05d644TGWRX2Gkpr8NeVS1O1InZf2y56R9lP3K7zUbQ0GXtumMn6D7iD0fzc0pCOCfd2iKjGq/XoeuBuE9qOh+U0DPnYRUty0Q1hCwfbuBnwxv0WctGvO1hL99n/uGrLEaJOjGGdqW4QVFMxdDr224kpl6oTYLVxFdF+cOpwgV18PJVpWBYQVubMYwEFHcoZaQF8L1aeZs9Lrjyjttj12ErpNTVD6/N93tgQ/P/Wr0f9DP0ovXJ6T3TVrxMe29mnfwy8FWdqQvtq3S0ggYweYeCCLnbehhtQ4Xr/dC1XujRgmygKXMRfYrJ//xBySXBxNsFu1M3MDtX/nj7cgU9BF7ZiTyBTqxpyxGiSv411BavW+L1yq1RjObmOYZUYKhDei2H2ipeVjrFBzYJmbYQebSF8GrhaZA== 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 2/25/25 19:45, Brendan Jackman wrote: > As documented in the comment this underflow should not happen. The > locking has indeed changed here since the comment was written, see the > migratetype hygiene patches[0]. However, those changes made the locking > _safer_, so the underflow _really_ shouldn't happen now. So upgrade > the comment to a warning. > > [0] https://lore.kernel.org/all/20240320180429.678181-7-hannes@cmpxchg.org/T/#m3da87e6cc3348a4640aa298137bc9f8f61b76c84 > > Signed-off-by: Brendan Jackman Reviewed-by: Vlastimil Babka Thanks! > --- > mm/page_alloc.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 5d8e274c8b1d500d263a17ef36fe190f60b88196..715a9cfe162090cca9eb819a34c64f9a1c6db29a 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3095,6 +3095,7 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac, > if (!page) > continue; > > + size = max(pageblock_nr_pages, 1UL << order); > /* > * It should never happen but changes to > * locking could inadvertently allow a per-cpu > @@ -3102,8 +3103,8 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac, > * while unreserving so be safe and watch for > * underflows. > */ > - size = max(pageblock_nr_pages, 1UL << order); > - size = min(size, zone->nr_reserved_highatomic); > + if (WARN_ON_ONCE(size > zone->nr_reserved_highatomic)) > + size = zone->nr_reserved_highatomic; > zone->nr_reserved_highatomic -= size; > > /* > > --- > base-commit: 0c789105c9d6c65777c995f4935f2e119d5a31a5 > change-id: 20250225-warn-underflow-7ab0069182e2 > > Best regards,