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Wed, 28 May 2025 20:52:46 -0700 (PDT) MIME-Version: 1.0 References: <20250515032226.128900-1-npache@redhat.com> In-Reply-To: From: Nico Pache Date: Wed, 28 May 2025 21:52:20 -0600 X-Gm-Features: AX0GCFsiYEJ1VuiCFlFESTf-xqRr1WAwbgRTyelRq-SxIdDhpm-aFp66aQ0MKqc Message-ID: Subject: Re: [PATCH v7 00/12] khugepaged: mTHP support To: Baolin Wang Cc: linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, 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 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: aV2PA5jjGu040KTWYeV3KuCzm2JJsy7kfiRv4kdna2M_1748490767 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 56669100004 X-Stat-Signature: s6aj8inyrnhuwgnrqd4xyms7dhoikcxm X-Rspam-User: X-HE-Tag: 1748490769-12802 X-HE-Meta: U2FsdGVkX1+2wMpDeiK+G02CTyCuzbcYQstSGauTQqrNDBt2TyB4g8lpftQyrmh2o6gqbSF6i0dUN04jYUFfqfd3eJb3GGLdWA/X6zlgBSG5s8fzsy5lkhmhfrvYnDwyDZT83v7jl2guq/ZVY6Ab/W/xKcAAfvi1Q1x1JOKAt3VcIxv7VGuAn1cvKSYLjFpBT5E57UvZMffJXuxZDylW3g0lqwIMPnbrzSciBVdMzLIBHMfJRRtH6pcSIEGO/4d90Hkmle2KEBtR59zPXSFYfOlwDiqoyE4rDoDp9Ht4gdTsJzFTMCzCd1321pKRVXQ8DOPrQgNMLWR8m6Df7FME6fY2Gm2/KloiExbyz1EpluV2AVLwtWHOWFX7Ta4Iz0DO/WAeljI7SSs7OJyN3va7xuVvawW7w2CSSO+O9eVVVZU/GODKzjw+FnFcSCLsumnd59Giuc5kUACOU09O9HCu0FwYwSsSX19LHee2DfaVJiLvyfy4nFDFiBYqoWXoh9BqMRr6cc5RsIym4Ixmqar9qyLAa3qnhKUa2Ty0HFOmAyI0Cay0jUFQqr0fDNvbyNAHd7M9YCeWMu0b77xp4bhZBlQOPUX6mEaD9f6vh2NaKGO3tsxlxWjcEOv1GeaBaM47YIITmv2tMOVPIIkA7Ltc5unV8TnXDT69qmWN1tDIMNCeTtjWxLPkix3z8tFkgY5a/rPTFiBNlNs8eCoeJYQStO+U7Fnqmw3Kk5I4UTdcx19PSJeVqnMnoMk44tzWogpskw6MFQr9joqPKJR9WmbSCXPAIiJ35tzoOuYX1l90nLkKqFwRI9CTpFenI/LC1nhUdnw84eq9bW7imv2i9uR43x5FN4i4uXZfBpXIZMDUfvtSBeQtL5EgbrmMHG1ysTQwLPqlMKnjpiKAwHc/+0kof+47OCmPqw6e7i0ZNtsHlj28cYRVsYzufooROpv3ZfNqdLwaHAIxEjFuqUAXE5t 3gbP+r4+ 8NcO79ELP2uUDOMH3Ty5fKH4DDHEIebUq5uTE4UmTTjnrs3fOLB6Y8blC+bUhSBZzaslpKg9/CVHJU3Qq4kdn8JwshBgy3iE7jsAaluRazdj7cr2lm/hvFCrKcwgqVKnQG3LVuDT4iBGiUt2+i8fJkFJtcpU30/rpsV4sHPdDFhG7NK5h0xWZy4F+c4gVif1OhQgRecsnpDYXcZlyvvLTsslQf+Spwdu3Gb2Om99r9wLGFFg28HdJUqOzPxlNrCOp+9p2di7Tn+n7O4kzdIXV7V3f2h7qzXULILRSzeynAPypBX4JGLKOsKJ+IV7iTti/vmEoHmMRpn7Yvd5Zke5XUjiGZP23851tMYfcKmEbS7TW29KlsYmP3Xxsag== 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 Wed, May 28, 2025 at 6:39=E2=80=AFAM Baolin Wang wrote: > > > > On 2025/5/15 11:22, Nico Pache wrote: > > The following series provides khugepaged and madvise collapse with the > > capability to collapse anonymous memory regions to mTHPs. > > > > To achieve this we generalize the khugepaged functions to no longer dep= end > > on PMD_ORDER. Then during the PMD scan, we keep track of chunks of page= s > > (defined by KHUGEPAGED_MTHP_MIN_ORDER) that are utilized. This info is > > tracked using a bitmap. After the PMD scan is done, we do binary recurs= ion > > on the bitmap to find the optimal mTHP sizes for the PMD range. The > > restriction on max_ptes_none is removed during the scan, to make sure w= e > > account for the whole PMD range. When no mTHP size is enabled, the lega= cy > > behavior of khugepaged is maintained. max_ptes_none will be scaled by t= he > > attempted collapse order to determine how full a THP must be to be > > eligible. If a mTHP collapse is attempted, but contains swapped out, or > > shared pages, we dont perform the collapse. > > > > With the default max_ptes_none=3D511, the code should keep its most of = its > > original behavior. To exercise mTHP collapse we need to set > > max_ptes_none<=3D255. With max_ptes_none > HPAGE_PMD_NR/2 you will > > experience collapse "creep" and constantly promote mTHPs to the next > > available size. This is due the fact that it will introduce at least 2x > > the number of pages, and on a future scan will satisfy that condition o= nce > > again. > > > > Patch 1: Refactor/rename hpage_collapse > > Patch 2: Some refactoring to combine madvise_collapse and khugepage= d > > Patch 3-5: Generalize khugepaged functions for arbitrary orders > > Patch 6-9: The mTHP patches > > Patch 10-11: Tracing/stats > > Patch 12: Documentation > > When I tested 64K mTHP collapse and disabled PMD-sized THP, I found that > khugepaged couldn't scan and collapse 64K mTHP. I send out two fix > patches[1], and with these patches applied, 64K mTHP collapse works > well. I hope my two patches can be folded into your next version series > if you think there are no issues. Thanks. Thank you for looking into that and fixing it, I had originally decided to only allow khugepaged to collapse to mTHP if the PMD size was enabled as well. It was on my todo list :) I'll work on adding your patches to my set, and do some proper testing again! > > [1] > https://lore.kernel.org/all/ac9ed6d71b439611f9c94b3506a8ce975d4636e9.1748= 435162.git.baolin.wang@linux.alibaba.com/ >