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Thu, 5 Nov 2026 07:26:45 -0500 (EST) Date: Thu, 5 Nov 2026 12:26:44 +0000 From: Kiryl Shutsemau To: Usama Arif Cc: Joanne Koong , akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, baohua@kernel.org, hannes@cmpxchg.org, alex@ghiti.fr, ziy@nvidia.com, baolin.wang@linux.alibaba.com, liam@infradead.org, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, lance.yang@linux.dev, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, willy@infradead.org, linux-mm@kvack.org Subject: Re: [PATCH v4 3/4] mm/huge_memory: add a per-order counter for underused splits Message-ID: References: <20261103212004.1356327-1-joannelkoong@gmail.com> <20261103212004.1356327-4-joannelkoong@gmail.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: fokc3d1r3msujhx4ki57kzroje6oeiid X-Rspamd-Server: rspam01 X-Rspam-User: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Queue-Id: 260D080004 X-HE-Tag: 1793881614-722452 X-HE-Meta: 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 K8f1yO04 DwswbuSEEgH8tIcE49ZSbiyxKC0JrN58DRZkCoGeSLWDS8YqhSp9R6I4aiSBsJZcnmWRi8YmcSM6BuCBiI0i4WMwgXNC2wWW3q+51jirad6UB9JSGhC4e1edd3wbp7fcTlH1kDMs7Yvme5satdtshBNY1wDIqxfpXwbT7EOiWjrBo0NL60wl/o+d5Ej8kt25wwgYUT77lySThCnt9iTYnnYQgysKviTHS3CCfjwmaQfieZjMUFLugfD+Nxs0bEhQkyKB14yXv9i0984kRgWAhwcH0/+Ya7t6VA7QNvzBun44hB9BU6EOQIe8vp+iMwjBANZ2GtWKfUV7BOL+ettmbN2ta2Wq3CXv3jBHyFJ73Kafu+Bc7UYl8vOT30A== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Tue, Nov 03, 2026 at 10:20:43PM +0000, Usama Arif wrote: > > > On 03/11/2026 21:20, Joanne Koong wrote: > > thp_underused_split_page counts every folio that the deferred split > > shrinker splits for being underused. Today that is only ever a > > PMD-sized folio, but a later patch queues anonymous mTHP folios for > > underused splitting too, at which point this counter would start > > counting mTHP splits as well. > > > > thp_underused_split_page could then end up larger than thp_split_page, > > and there would be no per-order count of underused splits. That doesn't > > match how the other THP split stats work. In /proc/vmstat, > > thp_split_page and thp_deferred_split_page only count PMD-sized folios. > > Splits of every size, PMD included, are counted per order in the split > > and split_deferred stats under hugepages-/stats/. > > > > Do the same for underused splits. Only count PMD-sized folios in > > thp_underused_split_page, and add a per-order split_underused stat that > > counts underused splits of every size. The folio's order has to be read > > before splitting it, since the folio is no longer large once the split > > succeeds. > > > > There is no functional change to thp_underused_split_page yet, as only > > PMD-sized folios are split for being underused today. > > > > Suggested-by: Kiryl Shutsemau > > Signed-off-by: Joanne Koong > > --- > > Documentation/admin-guide/mm/transhuge.rst | 6 ++++++ > > include/linux/huge_mm.h | 1 + > > mm/huge_memory.c | 10 ++++++++-- > > 3 files changed, 15 insertions(+), 2 deletions(-) > > > > diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst > > index b187d618452f..6f2d92a2a556 100644 > > --- a/Documentation/admin-guide/mm/transhuge.rst > > +++ b/Documentation/admin-guide/mm/transhuge.rst > > @@ -719,6 +719,12 @@ split_deferred > > it would free up some memory. Pages on split queue are going to > > be split under memory pressure, if splitting is possible. > > > > In this same commit, would you mind also doing s/THP/PMD mapped THP/ in > thp_underused_split_page section in /proc/vmstat section? PMD-size, not PMD-mapped. But yes, it would be nice to update. With that updated, feel free to use my Reviewed-by: Kiryl Shutsemau (Meta) -- Kiryl Shutsemau / Kirill A. Shutemov