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d=linux-foundation.org; s=korg; t=1694374416; bh=dX0snYQ5v39lGdN7KQzd0K/UxL2B6SP53/xbYKcI+vc=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=zwp9u4iwtP+uZQXd8KqiTBRa/KExQmJiUWwkKdTXrGjw86L8c1YclTnm4bPIiJaza efWGAZILsxJ3sB/vxNfnRZ+H41OKG5q6zxVwBW4qJ1kK0p5+CUOfzIw1sC8DGZbMQf /yIRO9OhC1UgORONb9mWgQqVd1ULSKQRoWatgu1E= Date: Sun, 10 Sep 2023 12:33:35 -0700 From: Andrew Morton To: Jiexun Wang Cc: brauner@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, falcon@tinylab.org Subject: Re: [PATCH 1/1] mm/madvise: add cond_resched() in madvise_cold_or_pageout_pte_range() Message-Id: <20230910123335.36ebf58e46628eeffef612c3@linux-foundation.org> In-Reply-To: <95d610623363009a71024c7a473d6895f39f3caf.1694219361.git.wangjiexun@tinylab.org> References: <95d610623363009a71024c7a473d6895f39f3caf.1694219361.git.wangjiexun@tinylab.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: DC5721C002A X-Stat-Signature: a7o8n6z87qoqarq5zc8iiggyutn8kgpq X-Rspam-User: X-HE-Tag: 1694374419-7240 X-HE-Meta: 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 Cs3X1QoC 3fZYJDYrs0pledfQx1HNmOubox5mL2nFFZb9cVdrFhJI2d9EALcHqL3yrsJ1Or/SPc4VLp8aOuSqbB8DbjslvC+SzBOUEFHI0aoEruDz+Kk+20PGx7OdNtX1Q3OHorW9yRd/ugR1G1hJ+w4GixQZ+yS3AwyRJ9zUPXgf0UeD0pZ0/vX4eRA4jDgl0mhPd63ZkBx4tf6DFFbWvxAyi1ImEQeuiSoXjiYHxVDoHRf8rQHaHPrQ+xEwpexAS+DPNy5d50UShiJNwddCGjJ+mlvKrMKIMIozJQuFTKpP1q0TWDEeOWl6HyI2+cxbkRryvTx9uL+naxgr7PNYkLXS75XpbSskerLYDHmuOBwphGVJkE07NZSvCYf4f1VmU6NXEK+Q8xqGlpt3uZ64ljRIj+Mdfsl2sRmgiyvb4I5sB5U/VoG+IhW2na/QskeSUJw== 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: On Sat, 9 Sep 2023 13:33:08 +0800 Jiexun Wang wrote: > Currently the madvise_cold_or_pageout_pte_range() function exhibits > significant latency under memory pressure, which can be effectively > reduced by adding cond_resched() within the loop. > > When the batch_count reaches SWAP_CLUSTER_MAX, we reschedule > the task to ensure fairness and avoid long lock holding times. > > ... > > @@ -441,6 +443,13 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd, > arch_enter_lazy_mmu_mode(); > for (; addr < end; pte++, addr += PAGE_SIZE) { > ptent = ptep_get(pte); > + > + if (++batch_count == SWAP_CLUSTER_MAX) { > + pte_unmap_unlock(start_pte, ptl); > + cond_resched(); > + start_pte = pte_offset_map_lock(mm, pmd, addr, &ptl); > + batch_count = 0; > + } > > if (pte_none(ptent)) > continue; I doubt if we can simply drop the lock like this then proceed as if nothing has changed while the lock was released. Could be that something along these lines: @@ -434,6 +436,7 @@ huge_unlock: regular_folio: #endif tlb_change_page_size(tlb, PAGE_SIZE); +restart: start_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl); if (!start_pte) return 0; @@ -441,6 +444,15 @@ regular_folio: arch_enter_lazy_mmu_mode(); for (; addr < end; pte++, addr += PAGE_SIZE) { ptent = ptep_get(pte); + + if (++batch_count == SWAP_CLUSTER_MAX) { + batch_count = 0; + if (need_resched()) { + pte_unmap_unlock(start_pte, ptl); + cond_resched(); + goto restart; + } + } if (pte_none(ptent)) continue; would work, but more analysis would be needed.