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Received: from 30.25.222.148(mailfrom:hsiangkao@linux.alibaba.com fp:SMTPD_---0W64.LOy_1715182848) by smtp.aliyun-inc.com; Wed, 08 May 2024 23:40:51 +0800 Message-ID: <52f9e300-4ab9-43c1-abae-cbe3da27e5b0@linux.alibaba.com> Date: Wed, 8 May 2024 23:40:48 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] mm/vmalloc: fix vmalloc which may return null if called with __GFP_NOFAIL To: Hailong Liu Cc: akpm@linux-foundation.org, Michal Hocko , urezki@gmail.com, hch@infradead.org, lstoakes@gmail.com, 21cnbao@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, xiang@kernel.org, chao@kernel.org, Oven References: <20240508125808.28882-1-hailong.liu@oppo.com> <404add29-2d3f-45db-9103-0c5b66fb254e@linux.alibaba.com> <20240508144321.ymnhn54daaabalhe@oppo.com> <90a127e5-d884-44b5-bb76-773a7485c2f1@linux.alibaba.com> <20240508153136.x4rxildsgza234uv@oppo.com> From: Gao Xiang In-Reply-To: <20240508153136.x4rxildsgza234uv@oppo.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 929B614002B X-Stat-Signature: dkobrjuzmfw58uhj7sr81ip3b38cyxec X-Rspam-User: X-HE-Tag: 1715182856-641908 X-HE-Meta: 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 OWaQypdp lRIrC1lV3v/toHbPZLU61bK29gaB4LwLsaB7BbVjHdyAm23t8xXWzyATqzSaQY7puZwhBlcUl0dDx2RPy7327g6SGuYyJOXTrwKe07pnkPxtapjXWBOB5/1TXSpa+Jm29E7RJSBt/CDhNk4PPyBr3y0oSYluH+MDUvwsraEcoKJsA2P7iI1/jQV+HF+ZyIHH/ZRFsMh+VO6bsa9puIGfld1Bf/rYLHs7S3DljgMz6VwvWeL1cBJEKExV870x5ef259zkkZNkEMwy2Q+Ra4ccMLY+L7/s5aoL0ZjoSH/uPrNlq2XWiYUDFfnT6Y6TID7uRnz6vpk3bB4rAUuk2xYLCLlz2aDsjpHZcxmuY7cpqEN+i5JeEroRQCuUN7EhEyUkelzHtWQ6mf/Nba68NgPixBxLjE6/+JBvxm4q1uvHP0G0932d+w/AKeKW5mNOUjSjlvj+EGzm1AHf1jaOe2SVli1IU0w== 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 2024/5/8 23:31, Hailong Liu wrote: > On Wed, 08. May 23:10, Gao Xiang wrote: >> Hi, >> >> On 2024/5/8 22:43, Hailong Liu wrote: >>> On Wed, 08. May 21:41, Gao Xiang wrote: >>>> >>>> +Cc Michal, >>>> >>>> On 2024/5/8 20:58, hailong.liu@oppo.com wrote: >>>>> From: "Hailong.Liu" >>>>> >>>>> Commit a421ef303008 ("mm: allow !GFP_KERNEL allocations for kvmalloc") >>>>> includes support for __GFP_NOFAIL, but it presents a conflict with >>>>> commit dd544141b9eb ("vmalloc: back off when the current task is >>>>> OOM-killed"). A possible scenario is as belows: >>>>> >>>>> process-a >>>>> kvcalloc(n, m, GFP_KERNEL | __GFP_NOFAIL) >>>>> __vmalloc_node_range() >>>>> __vmalloc_area_node() >>>>> vm_area_alloc_pages() >>>>> --> oom-killer send SIGKILL to process-a >>>>> if (fatal_signal_pending(current)) break; >>>>> --> return NULL; >>>>> >>>>> to fix this, do not check fatal_signal_pending() in vm_area_alloc_pages() >>>>> if __GFP_NOFAIL set. >>>>> >>>>> Reported-by: Oven >>>>> Signed-off-by: Hailong.Liu >>>> >>>> Why taging this as RFC here? It seems a corner-case fix of >>>> commit a421ef303008 >>>> >>>> Thanks, >>>> Gao Xiang >>>> >>> >>> Hi Gao Xiang: >>> >>> RFC here to wait for a better way to handle this case :). >>> IMO, if vmalloc support __GFP_NOFAIL it should not return >>> null even system is deadlock on memory. >> >> The starting point is that kmalloc doesn't support __GFP_NOFAIL >> if order > 1 (even for very short temporary uses), see: >> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/page_alloc.c?h=v6.8#n2896 >> >> but it is possible if we have such page pointer array (since two >> (order-1) pages can only keep 1024 8-byte entries, it can happen >> if compression ratios are high), and kvmalloc(__GFP_NOFAIL) has >> already been supported for almost two years, it will fallback to >> order-0 allocation as described in commit e9c3cda4d86e >> ("mm, vmalloc: fix high order __GFP_NOFAIL allocations"). >> >> With my limited understanding, I'm not sure why it can cause >> deadlock here since it will fallback to order-0 allocation then, >> and such allocation is just for short temporary uses again >> because kmalloc doesn't support order > 1 short memory >> allocation strictly. >> > > deadlock on memory meands there is a memory leak causing > system to be unable to allocate memory not actual > *deadlock*. Where is memory leak? If it's caused by kvmalloc(__GFP_NOFAIL) callers, then it's bugs of callers and we should fix the callers. Also why kmalloc(__GFP_NOFAIL) (for example, also order-0 allocation) differs? Thanks, Gao Xiang > >> Thanks, >> Gao Xiang >> > > -- > > Best Regards, > Hailong.