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[109.81.86.254]) by smtp.gmail.com with UTF8SMTPSA id 5b1f17b1804b1-45b7e887fdcsm145730905e9.13.2025.09.01.00.41.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 01 Sep 2025 00:41:21 -0700 (PDT) Date: Mon, 1 Sep 2025 09:41:20 +0200 From: Michal Hocko To: zhongjinji Cc: rientjes@google.com, shakeel.butt@linux.dev, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, liam.howlett@oracle.com, lorenzo.stoakes@oracle.com, surenb@google.com, liulu.liu@honor.com, feng.han@honor.com, tianxiaobin@honor.com, fengbaopeng@honor.com Subject: Re: [PATCH v6 2/2] mm/oom_kill: The OOM reaper traverses the VMA maple tree in reverse order Message-ID: References: <20250829065550.29571-1-zhongjinji@honor.com> <20250829065550.29571-3-zhongjinji@honor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250829065550.29571-3-zhongjinji@honor.com> X-Stat-Signature: gkbj9bw8uqk75ti6i7u85myisamjcgpt X-Rspam-User: X-Rspamd-Queue-Id: 5A78940004 X-Rspamd-Server: rspam01 X-HE-Tag: 1756712483-926772 X-HE-Meta: U2FsdGVkX1/2Qf0QZv/6CfDz08GcixBK1azCuvrunIm+L2sDGgrBGA4J9E0EPfMvwQgjHllU39WegDWKHTsUA0UotMLDeZ/Q6MklZQBkuudr4t2cf52quY764yiA1ansA2L7Wdn75Kl3kn0mji6rnf7igH4Icm2TnMxPVKfydSTEUGK14mQPxBKSLyHtsk/SxXA3XVjl55Co+XCtQAU53jpnskIpO1Gnx6EFJwCC8WHs6S+aP0eQ6mHfL+qhqw03KqChFlSVxqBP4Tco530MPsx/9p8LVJCFHM00iOTVZ1nYN6oI+Ms+1+3ouU/XOgbgRO/jTW0ZGwdhWHQ++q+c6ozopR8CH0OnX0mKL/Jr7sgYs505gzFEPRIs+Y1MORfYCgyWN7kFSHkGz7wXGeycsRyPXn2oYkkgx2N67eZy4MKs1tHbSW1oHO/12+ROsOM3D69Sak6JvnQC2JS4a60u3fva0br5R4AMeG61BZGEc35M0pw4i0YF3Xpv2d7fmDyJbmfj47WCSDVLf1bv64obTEFDI4SxEYKeR4Qpca+3+Lbn2kHLMC6DNJYv1vKtGjK0bWmvou3RR7MwpfySaEweIYvpkZZFQh14Q7oXtq+JdaLaoYpkZleR0T2F1YBoO8Y8e+lKX++TF9+1KDuUHB9K9ffXtdFDyoqX0Ms28PcjapUJYibUcNvRTOGIQa7VImb2r3+WJ0Pn/f703K3LtmOE3LAI2x85cJIvMa5DytKwOia+wTrsVPNACcVNPhIe2yxQN1H8ZF7HFFNtgLHoWTAc+vEaMC4NVUNwYavYfe+rstdQSMBzIvq3Xtl+oa29vKNDq+k9E4xbxm+depX9AKNwR1si2zdkl8yTUvVy1KVwvkWVZBC7DwIQ4715kJ/0s24rcUsyBSIiCsPqKnm5LPtojr2/X1rw8s2ZdDLGapwmV/D/NnWzsLtAxzo3bRerQuP8VUwJyDZarL5jGo8NtJJ hvFlAo3j u55+B/Xz8ifeYAuK9ZFKivudxek0dVv8nGL3R3hy2IVKS2sGkixxMkmeg5I2YaCGp6t1uGfIu+KheH3/YbZ0aN1xAMSf6AqL5nSCR0XLjjdQiM7JAp8jKbpgCKnNcaGgo0iY4x07U3iC3U+YvWGebs0bbzoKRA19mDUx26JYMuJ447KG2Zq2VvMYsJwOd1tSCwgPkND5P4SwyWZrfwuWo1gUTu4hudi7m4S8C1QJMUmw/Z2H9FhSC3liymQYCF0PiQ8DhbEKZVItRZiFwpdBq1Jri5DpjKmdIxES8HkYoTU2bP7qGnELNEohjIi/pFjn0ClmrxOcVU5S5Zig6SCqvhulMmPCTElqScuLEzo6kG8le6tj/1b1t/nCNyOuc5d4To1xAM8y8rXEUpZTyKx5tlmIYhxx7LPg13RFWqsMBQqqPizCp4YnkBNKoWWqdeFQgOwFEXfh3ChtIzVGl8ehkUTq1umgBKQU4O+eB 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 Fri 29-08-25 14:55:50, zhongjinji wrote: > When a process is OOM killed without reaper delay, the oom reaper and the > exit_mmap() thread likely run simultaneously. They traverse the vma's maple > tree along the same path and may easily unmap the same vma, causing them to > compete for the pte spinlock. > > When a process exits, exit_mmap() traverses the vma's maple tree from low > to high addresses. To reduce the chance of unmapping the same vma > simultaneously, the OOM reaper should traverse the vma's tree from high to > low address. > > Reported-by: tianxiaobin > Reported-by: fengbaopeng > > Signed-off-by: zhongjinji The changelog could be improved because it is a bit confusing at this stage. I haven't payed a close attention to previous discussion (sorry) but there are two Reported-bys without any actual problem statement (sure contention could happen but so what? What was the observed behavior). Also the first paragraph states that "without reaper delay" there is a problem but the only situation we do not have a dealay is when the task is frozen and there is no racing there. As already said in the previous response I think this makes conceptual sense especially for oom victims with large address spaces which take more that the OOM_REAPER_DELAY to die. Maybe you want to use that as a justiciation. My wording would be " Although the oom_reaper is delayed and it gives the oom victim chance to clean up its address space this might take a while especially for processes with a large address space footprint. In those cases oom_reaper might start racing with the dying task and compete for shared resources - e.g. page table lock contention has been observed. Reduce those races by reaping the oom victim from the other end of the address space. " Anyway, with a changelog clarified. Acked-by: Michal Hocko > --- > mm/oom_kill.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index a5e9074896a1..01665a666bf1 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -516,7 +516,7 @@ static bool __oom_reap_task_mm(struct mm_struct *mm) > { > struct vm_area_struct *vma; > bool ret = true; > - VMA_ITERATOR(vmi, mm, 0); > + MA_STATE(mas, &mm->mm_mt, ULONG_MAX, ULONG_MAX); > > /* > * Tell all users of get_user/copy_from_user etc... that the content > @@ -526,7 +526,12 @@ static bool __oom_reap_task_mm(struct mm_struct *mm) > */ > set_bit(MMF_UNSTABLE, &mm->flags); > > - for_each_vma(vmi, vma) { > + /* > + * When two tasks unmap the same vma at the same time, they may contend > + * for the pte spinlock. To reduce the probability of unmapping the same vma > + * as exit_mmap, the OOM reaper traverses the vma maple tree in reverse order. > + */ > + mas_for_each_rev(&mas, vma, 0) { > if (vma->vm_flags & (VM_HUGETLB|VM_PFNMAP)) > continue; > > -- > 2.17.1 -- Michal Hocko SUSE Labs