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Thu, 5 Nov 2026 07:20:54 -0500 (EST) Date: Thu, 5 Nov 2026 12:20:53 +0000 From: Kiryl Shutsemau To: Joanne Koong Cc: akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, baohua@kernel.org, usama.arif@linux.dev, 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 1/4] mm/huge_memory: scale thp_underused() to the folio size Message-ID: References: <20261103212004.1356327-1-joannelkoong@gmail.com> <20261103212004.1356327-2-joannelkoong@gmail.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261103212004.1356327-2-joannelkoong@gmail.com> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: BA5842000F X-Stat-Signature: fa4mwq7jog589hwd1jqhb4w45is64kzh X-Rspam-User: X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1793881261-454871 X-HE-Meta: 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 DcYnWY5b w4jX6JiBVqiztOOK5s3KkU/WmXG1kS6Gmpjh0DkWyvAkn/eCT+DVJ5EhiLiqtTVq2c7IB36YzNngySq6+UiVEa8DCePfANdBXBFWQyfBT70MbtTs76SkceSrXPC0Af0tYUFyAGCxfbXm6OiYJQG6m+1ONNP9v+IzC/t/9h8njKP4J29iF9EBjZu6BDb7X/BzMOugBBpYCDzR7qWWwspJ2fRCNfZhvVWfUIXcMQD6ybFy344M092wXycZ3B3yyaNIJh1Cy8/3gfEuuCfbdXL0UJOWKVeEUFa/+Nkuqq/gGqwaahi/Yb5ZRVeLcoqyxuroxMAUhfMyb96vNFMsfVUVUJ3UHZuXTZg/TA+nZVmZ3pSwNZx3QiWhKcrK3hQ== 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 01:20:01PM -0800, Joanne Koong wrote: > thp_underused() decides whether a large folio on the deferred split list > is underused and should be split so that its zero-filled subpages can be > reclaimed. > > Today it only ever runs on PMD-sized folios, so it assumes that the > folio has HPAGE_PMD_NR pages and compares the zero-filled page count > directly against khugepaged_max_ptes_none. A later patch will queue > anonymous mTHP folios onto the deferred split list as well, at which > point that assumption will no longer hold. > > Make thp_underused() folio-size-aware, and scale > khugepaged_max_ptes_none proportionally to the number of pages in the > folio (eg every folio tolerates the same fraction of zero-filled pages > the user configured for a PMD-sized folio). > > khugepaged deliberately doesn't scale intermediate values when > collapsing to mTHP orders (to avoid the memory footprint creeping up > through repeated collapses), but if/when collapse later gains support > for intermediate values, a folio that khugepaged collapses won't then be > split right back by the shrinker (and vice versa) since both collapse > and split would use the same threshold for a given folio size. > > There is no functional change for PMD-sized folios, as for those, > nr_pages is HPAGE_PMD_NR. > > Suggested-by: Usama Arif > Signed-off-by: Joanne Koong Reviewed-by: Kiryl Shutsemau (Meta) -- Kiryl Shutsemau / Kirill A. Shutemov