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[188.147.112.12]) by smtp.gmail.com with ESMTPSA id t4sm20485749wrr.26.2020.09.14.03.07.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 14 Sep 2020 03:07:47 -0700 (PDT) From: mateusznosek0@gmail.com To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Mateusz Nosek , akpm@linux-foundation.org Subject: [RFC PATCH] mm/page_alloc.c: micro-optimization reduce oom critical section size Date: Mon, 14 Sep 2020 12:06:54 +0200 Message-Id: <20200914100654.21746-1-mateusznosek0@gmail.com> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Mateusz Nosek Most operations from '__alloc_pages_may_oom' do not require oom_mutex hold. Exception is 'out_of_memory'. The patch refactors '__alloc_pages_may_oom' to reduce critical section size and improve overall system performance. Signed-off-by: Mateusz Nosek --- mm/page_alloc.c | 45 ++++++++++++++++++++++++--------------------- 1 file changed, 24 insertions(+), 21 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index b9bd75cacf02..b07f950a5825 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3935,18 +3935,7 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order, .order = order, }; struct page *page; - - *did_some_progress = 0; - - /* - * Acquire the oom lock. If that fails, somebody else is - * making progress for us. - */ - if (!mutex_trylock(&oom_lock)) { - *did_some_progress = 1; - schedule_timeout_uninterruptible(1); - return NULL; - } + bool success; /* * Go through the zonelist yet one more time, keep very high watermark @@ -3959,14 +3948,17 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order, ~__GFP_DIRECT_RECLAIM, order, ALLOC_WMARK_HIGH|ALLOC_CPUSET, ac); if (page) - goto out; + return page; + + /* Check if somebody else is making progress for us. */ + *did_some_progress = mutex_is_locked(&oom_lock); /* Coredumps can quickly deplete all memory reserves */ if (current->flags & PF_DUMPCORE) - goto out; + return NULL; /* The OOM killer will not help higher order allocs */ if (order > PAGE_ALLOC_COSTLY_ORDER) - goto out; + return NULL; /* * We have already exhausted all our reclaim opportunities without any * success so it is time to admit defeat. We will skip the OOM killer @@ -3976,12 +3968,12 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order, * The OOM killer may not free memory on a specific node. */ if (gfp_mask & (__GFP_RETRY_MAYFAIL | __GFP_THISNODE)) - goto out; + return NULL; /* The OOM killer does not needlessly kill tasks for lowmem */ if (ac->highest_zoneidx < ZONE_NORMAL) - goto out; + return NULL; if (pm_suspended_storage()) - goto out; + return NULL; /* * XXX: GFP_NOFS allocations should rather fail than rely on * other request to make a forward progress. @@ -3992,8 +3984,20 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order, * failures more gracefully we should just bail out here. */ + /* + * Acquire the oom lock. If that fails, somebody else is + * making progress for us. + */ + if (!mutex_trylock(&oom_lock)) { + *did_some_progress = 1; + schedule_timeout_uninterruptible(1); + return NULL; + } + success = out_of_memory(&oc); + mutex_unlock(&oom_lock); + /* Exhausted what can be done so it's blame time */ - if (out_of_memory(&oc) || WARN_ON_ONCE(gfp_mask & __GFP_NOFAIL)) { + if (success || WARN_ON_ONCE(gfp_mask & __GFP_NOFAIL)) { *did_some_progress = 1; /* @@ -4004,8 +4008,7 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order, page = __alloc_pages_cpuset_fallback(gfp_mask, order, ALLOC_NO_WATERMARKS, ac); } -out: - mutex_unlock(&oom_lock); + return page; } -- 2.20.1