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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-42ba642593asm163335275e9.39.2024.09.02.00.40.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 02 Sep 2024 00:40:29 -0700 (PDT) Message-ID: <6f14bc6d-f01b-48ad-b928-1dc2c7e43ec5@redhat.com> Date: Mon, 2 Sep 2024 09:40:28 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 3/3] mm: warn about illegal __GFP_NOFAIL usage in a more appropriate location and manner To: Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org, virtualization@lists.linux.dev Cc: 42.hyeyoo@gmail.com, cl@linux.com, hailong.liu@oppo.com, hch@infradead.org, iamjoonsoo.kim@lge.com, mhocko@suse.com, penberg@kernel.org, rientjes@google.com, roman.gushchin@linux.dev, torvalds@linux-foundation.org, urezki@gmail.com, v-songbaohua@oppo.com, vbabka@suse.cz, laoar.shao@gmail.com References: <20240830202823.21478-1-21cnbao@gmail.com> <20240830202823.21478-4-21cnbao@gmail.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Stat-Signature: z7oc8wiw776c6wir38xz7rzd9zg938m6 X-Rspamd-Queue-Id: A9E021C0011 X-Rspamd-Server: rspam11 X-HE-Tag: 1725262835-316938 X-HE-Meta: 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 ZSwuhZIu DAOyxeCDZZ1ngczj+7japzH2Sszvo9z3nQL0GM94RLNdUXESMKF59TrHytsG3MbHDUacHBPd/3wZLRiwib/gdDa0Pf7P1kI46UwJpLJQScr4mlvtpFxlfIaD5ibMWvCKdemgPtKEUPZfxmfTjbtCTIgHQEQ+dBJXNnpFxvNYgsV3CW71TqdmCz+H4bJL/TRD6u8d5/sLFM6QPOYCwl+6aChNRD4fupYUb8RBnNYxv7p33ay/4EX7ER4Awv/ZoNT3Q2LQqwZl7pwJ7K32lh7/W5upLeUn5q8uM/yQk+PpoC5LctAAOwzlPk8ukOVicCiuoh4vAUGYJUFtTCWYetaGHIQsgSQs9wCmdNZvRwoswGyA0jBc8+2Ejet+4gzhs9yi3eoCiT2cmvMUgfXdBg4W0iWUeCPZ6XfWPh5+IOCeMAvTYVMx7kkLfTfrU1VjtHQ0/TlClXJBDQUdB/almlC1iJt0axX7oPRlSIKKw+mPEiO0HJhmFB8Pfc2I0LmlsMolpfk9SyFK/Mj15iXqiPWxVbmcbfIjmcxvEqZqru51OJI2Pt62xrx12QOE+McjXzgOTF0EhyRx7VbWqf5MQGBmWklj907yk78DYyCwuIzPTbcwZbljiWw06+KN5ZDQU+Jo6xFfzeVHVv9UXG3m0ODtrI9uiQ5BPDrD4DTclzbMuw9Zgje0XGIGIFNaj180EFAeSzqW+zoX7HqBSAUy6edX83nCj5i2n5ruqggza 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 30.08.24 22:28, Barry Song wrote: > From: Barry Song > > Three points for this change: > > 1. We should consolidate all warnings in one place. Currently, the > order > 1 warning is in the hotpath, while others are in less > likely scenarios. Moving all warnings to the slowpath will reduce > the overhead for order > 1 and increase the visibility of other > warnings. > > 2. We currently have two warnings for order: one for order > 1 in > the hotpath and another for order > costly_order in the laziest > path. I suggest standardizing on order > 1 since it’s been in > use for a long time. > > 3. We don't need to check for __GFP_NOWARN in this case. __GFP_NOWARN > is meant to suppress allocation failure reports, but here we're > dealing with bug detection, not allocation failures. So replace > WARN_ON_ONCE_GFP by WARN_ON_ONCE. > > Suggested-by: Vlastimil Babka > Signed-off-by: Barry Song > --- > mm/page_alloc.c | 50 ++++++++++++++++++++++++------------------------- > 1 file changed, 25 insertions(+), 25 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index c81ee5662cc7..e790b4227322 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3033,12 +3033,6 @@ struct page *rmqueue(struct zone *preferred_zone, > { > struct page *page; > > - /* > - * We most definitely don't want callers attempting to > - * allocate greater than order-1 page units with __GFP_NOFAIL. > - */ > - WARN_ON_ONCE((gfp_flags & __GFP_NOFAIL) && (order > 1)); > - > if (likely(pcp_allowed_order(order))) { > page = rmqueue_pcplist(preferred_zone, zone, order, > migratetype, alloc_flags); > @@ -4175,6 +4169,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > { > bool can_direct_reclaim = gfp_mask & __GFP_DIRECT_RECLAIM; > bool can_compact = gfp_compaction_allowed(gfp_mask); > + bool nofail = gfp_mask & __GFP_NOFAIL; > const bool costly_order = order > PAGE_ALLOC_COSTLY_ORDER; > struct page *page = NULL; > unsigned int alloc_flags; > @@ -4187,6 +4182,25 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > unsigned int zonelist_iter_cookie; > int reserve_flags; > > + if (unlikely(nofail)) { > + /* > + * We most definitely don't want callers attempting to > + * allocate greater than order-1 page units with __GFP_NOFAIL. > + */ Acked-by: David Hildenbrand Should we also clarify that in the docs? Currently we have "Using this flag for costly allocations is _highly_ discouraged." We'd likely want to say something like "Allocating pages from the buddy with __GFP_NOFAIL and order > 1 is not supported." -- Cheers, David / dhildenb