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Tue, 25 Nov 2025 12:26:21 +0800 Date: Tue, 25 Nov 2025 12:26:19 +0800 From: Zhiheng Tao To: Lance Yang Cc: ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, shy828301@gmail.com, zokeefe@google.com, peterx@redhat.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, lorenzo.stoakes@oracle.com, "David Hildenbrand (Red Hat)" Subject: Re: [PATCH] mm/khugepaged: Fix skipping of alloc sleep after second failure Message-ID: <20251125042619.GA119062@i85a15111.eu95sqa> References: <1763965157-58413-1-git-send-email-junchuan.tzh@antgroup.com> <0f292735-4b13-417f-bc65-82cebd2040a3@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0f292735-4b13-417f-bc65-82cebd2040a3@linux.dev> User-Agent: Mutt/1.5.21 (2010-09-15) X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 888B218000C X-Stat-Signature: tex7q5zrgs3n6386xwh958aqophzypza X-Rspam-User: X-HE-Tag: 1764044784-457885 X-HE-Meta: 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 Q0OGdfYb l3sichfTh9Y8Dmc9a0DQOKdmgFrtfIIVo9SqjKllWsMy5uF4667X6CSW9fOiDr1NpuioRql1tLWVFc1j+xlPrQQP5sc82Od/PqTn78O8KS+SnQ4HnfdYVbZFZ0/pTGai8WkFiBEFvtP3bX+dsJR08pVYM4yDMR/wTy7cmAq5ReJIi3FI1oV85yjqon4h7M9S+fxM3f4bW0+E9hsoKvcYVQD36wMfjCkkPbEHcjz1FJTotFBQnXea5dTxmZrc7YfR7RBcv 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 Mon, Nov 24, 2025 at 05:27:23PM +0800, Lance Yang wrote: > > > On 2025/11/24 17:14, David Hildenbrand (Red Hat) wrote: > >On 11/24/25 07:19, Zhiheng Tao wrote: > >>In khugepaged_do_scan(), two consecutive allocation failures cause > >>the logic to skip the dedicated 60s throttling sleep > >>(khugepaged_alloc_sleep_millisecs), forcing a fallback to the > >>shorter 10s scanning interval via the outer loop > >> > >>Since fragmentation is unlikely to resolve in 10s, this results in > >>wasted CPU cycles on immediate retries. > > > >Why shouldn't memory comapction be able to compact a single THP in 10s? > > > >Why should it resolve in 60s? > > > >> > >>Reorder the failure logic to ensure khugepaged_alloc_sleep() is > >>always called on each allocation failure. > >> > >>Fixes: c6a7f445a272 ("mm: khugepaged: don't carry huge page to > >>the next loop for !CONFIG_NUMA") > > > >What are we fixing here? This sounds like a change that might be > >better on some systems, but worse on others? > > Seems like we're not honoring khugepaged_alloc_sleep_millisecs on the > second allocation failure... but is that actually a problem? > Is it more appropriate to honor the second allocation failure? It was a problem before commit c6a7f445a272 when khugepaged_pages_to_scan=512. > > > >We really need more information on when/how an issue was hit, and > >how this patch here really moves the needle in any way. > > +1 >