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Thu, 07 May 2026 23:27:55 -0700 (PDT) Message-ID: Date: Fri, 8 May 2026 14:27:49 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] cgroup/cpuset: move PF_EXITING check before __GFP_HARDWALL in cpuset_current_node_allowed() To: =?UTF-8?Q?Michal_Koutn=C3=BD?= Cc: longman@redhat.com, chenridong@huaweicloud.com, tj@kernel.org, hannes@cmpxchg.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260507105434.3266234-1-chenwandun@lixiang.com> Content-Language: en-US From: Wandun In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 5/7/26 20:33, Michal Koutný wrote: > On Thu, May 07, 2026 at 06:54:34PM +0800, Chen Wandun wrote: >> This makes it unreachable in the common case, so dying tasks can get >> stuck in direct reclaim or even trigger OOM while trying to exit, >> despite being allowed to allocate from any node. > (OTOH, the caused OOM could select this task and bypass the hardwall. So > this should only expedite but no unblock the exit path.) > >> Move the PF_EXITING check before __GFP_HARDWALL so that dying tasks >> can allocate memory from any node to exit quickly, even when cpusets >> are enabled. > This makes sense to me on its own (given other hardwall exemptions, > namely the commit c596d9f320aaf ("cpusets: allow TIF_MEMDIE threads to > allocate anywhere")). > > Acked-by: Michal Koutný > > > At first, I wondered whether this could happen on cpuset v2 -- it can -- > because only per-cpuset hardwalling is absent but the generic logic for > GFP_USER allocations is still meant to be in place. Nevertheless, it > occured to me we can spare callback_lock in this function (a separate > chaneg for cpuset_current_node_allowed()): > > --- a/kernel/cgroup/cpuset.c > +++ b/kernel/cgroup/cpuset.c > @@ -4213,6 +4213,9 @@ bool cpuset_current_node_allowed(int node, gfp_t gfp_mask) > if (current->flags & PF_EXITING) /* Let dying task have memory */ > return true; > > + if (is_in_v2_mode()) > + return true; > + Thanks for the suggestion! I'll send a separate patch for this optimization. Best regards, Wandun > /* Not hardwall and node outside mems_allowed: scan up cpusets */ > spin_lock_irqsave(&callback_lock, flags); > > Regards, > Michal