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b=fWG31X3D6NxMbW781vVTlUEzfZQzMK+udrmZ6fcvtEyJAArDn94woCcdJe4Wy3Fw4C6FE0tirdgTF3LA+BCTH2/DhLr6hRVW9swx8cccDMiOZbGbyVn8VbDRbfrC0M5+NXQROJ35ZIK3+x+w6AlLaUnZj7B9YoK/5AYK5Sdt1MU= Received: from 30.74.144.111(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0WjAe3gk_1752804891 cluster:ay36) by smtp.aliyun-inc.com; Fri, 18 Jul 2025 10:14:52 +0800 Message-ID: <85b2cfd8-4aeb-4e98-8065-b6594783de62@linux.alibaba.com> Date: Fri, 18 Jul 2025 10:14:51 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 09/14] khugepaged: avoid unnecessary mTHP collapse attempts To: Nico Pache , linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Cc: david@redhat.com, ziy@nvidia.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, ryan.roberts@arm.com, dev.jain@arm.com, corbet@lwn.net, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, akpm@linux-foundation.org, baohua@kernel.org, willy@infradead.org, peterx@redhat.com, wangkefeng.wang@huawei.com, usamaarif642@gmail.com, sunnanyong@huawei.com, vishal.moola@gmail.com, thomas.hellstrom@linux.intel.com, yang@os.amperecomputing.com, kirill.shutemov@linux.intel.com, aarcange@redhat.com, raquini@redhat.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, tiwai@suse.de, will@kernel.org, dave.hansen@linux.intel.com, jack@suse.cz, cl@gentwo.org, jglisse@google.com, surenb@google.com, zokeefe@google.com, hannes@cmpxchg.org, rientjes@google.com, mhocko@suse.com, rdunlap@infradead.org, hughd@google.com References: <20250714003207.113275-1-npache@redhat.com> <20250714003207.113275-10-npache@redhat.com> From: Baolin Wang In-Reply-To: <20250714003207.113275-10-npache@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 8EEA14000A X-Stat-Signature: cd734kyah93bgyfuhq39ujn1e157izxh X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1752804899-93712 X-HE-Meta: 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 5COII9D1 P9q6YkHL8dG44HDETJq3sLcEzl+0QaXX1xP89DKqCq8NSqEqlmomXm8/PEI6DGK68ajffM0VJqi6g/gUjHgJNV/83wmIpjFXIO9XN7NdszKR4W8WryYai0Q4Syjw8aa6CCUJVSatHBROhouQaJ5KKCo1o2JfrSg4dLQSKBi7pMe3LLBJOSmIv2o0y0WpXODpbuMeJtigYIPXFHWhfBMj9/MIiA8BqDMNMsh24HJafe6Tn2LqryHZIVlSxzM2X4xoZO9LjkDoVUHez7TuV+i7owxl+dojV5XxPZEyBaYvvIYpSTLyrw0NkByc6F4KVPttCvEJjMd4ifiMnOGAs0RJXW3a7SeHJC/kylcop5v3xZj06CLj2Jy8GsoVsQHH3RN6I+SfRDtT7NCvpDTacap0U5+ygboo2TH9pIQo4F566iFgPhJChnY9c6lR8CnyIcBGwcWI3cjg23ondkDc= 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 2025/7/14 08:32, Nico Pache wrote: > There are cases where, if an attempted collapse fails, all subsequent > orders are guaranteed to also fail. Avoid these collapse attempts by > bailing out early. > > Signed-off-by: Nico Pache > --- > mm/khugepaged.c | 17 +++++++++++++++++ > 1 file changed, 17 insertions(+) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index a701d9f0f158..7a9c4edf0e23 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -1367,6 +1367,23 @@ static int collapse_scan_bitmap(struct mm_struct *mm, unsigned long address, > collapsed += (1 << order); > continue; > } After doing more testing, I think you need to add the following changes after patch 8. Because when collapsing mTHP, if we encounter a PTE-mapped large folio within the PMD range, we should continue scanning to complete that PMD, in case there is another mTHP that can be collapsed within that PMD range. + if (ret == SCAN_PTE_MAPPED_HUGEPAGE) + continue; > + /* > + * Some ret values indicate all lower order will also > + * fail, dont trying to collapse smaller orders > + */ > + if (ret == SCAN_EXCEED_NONE_PTE || > + ret == SCAN_EXCEED_SWAP_PTE || > + ret == SCAN_EXCEED_SHARED_PTE || > + ret == SCAN_PTE_NON_PRESENT || > + ret == SCAN_PTE_UFFD_WP || > + ret == SCAN_ALLOC_HUGE_PAGE_FAIL || > + ret == SCAN_CGROUP_CHARGE_FAIL || > + ret == SCAN_COPY_MC || > + ret == SCAN_PAGE_LOCK || > + ret == SCAN_PAGE_COUNT) > + goto next; > + else Nit: the 'else' statement can be dropped. > + break; > } > > next: