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b=Ul8G+PLuHQzMqCcaTBmaiVFddbBPa6py0orboYcGagVbnzKGnPy11HZwDVoGQQ8p7 IgYkupOTJvpTkm/deSnZBZVDLf3+Hk3Ob5G9n4lvtPGzGvbQRGCPr9cyFC/vE5eDdH lrtsAVzHiOaq5+OmZo7JUmBlLNQZtnkHw8sQ+V3ae4Tr3bXUJSDJYcRDNVv6S7N8yw JK+J8nldKfrWDzdcZvz2bZBYOH1J4YLdiY85RItTeOpR1eMSTlmJBnp6YP3Msq5srF AM4378+2ZEdWxI7uVq/pvIy1+kZ46OauU5HpVwilRewwR0BxN5NtxUPL9AFVKpT1ZN Wb80PuYgS9kYw== From: SeongJae Park To: Stepanov Anatoly Cc: SeongJae Park , gutierrez.asier@huawei-partners.com, artem.kuzin@huawei.com, wangkefeng.wang@huawei.com, yanquanmin1@huawei.com, zuoze1@huawei.com, damon@lists.linux.dev, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v1 1/1] mm/damon: support MADV_COLLAPSE via DAMOS_COLLAPSE scheme action Date: Tue, 31 Mar 2026 17:54:01 -0700 Message-ID: <20260401005402.85833-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <716989f5-78d3-4e78-98ae-2bf3caa447a9@huawei.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 201CF14000F X-Stat-Signature: xhgq7a5fs1yuc4cegkc6547f48xnro91 X-Rspam-User: X-HE-Tag: 1775004845-804902 X-HE-Meta: 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 XEzqJqcU NvpAh6etGz6WGH4/bd4MSt/ZGViDV/RHl6102IgmJ+ypLvQcPKqnvpD9HpPTRN/O59hIOLx3DZDYeCb3fVL/VoO1nK3X8K4lHoluefqHw0/NZSkzH5jjGPzkuK7Sz6dQv/aDruGB+x1dBpPPH3G3VkKnovXo5IbE0zIlNoC7ClsHFibFGL/+29f4bLp2FeHKIhR01l8bYGnK1FJJVivVhe4J/AIoD3CzltS2wUbkgScQWCoZ0Jt7/3b4nWSQWVD/3YTDVJVqVDxLZQRirUjE0CN+XUgHnUiAIlL+tyVCZsuVf/ZFt0tDE//fOMkIuhAnCZaQoUODJwuigFShKq4GOk7jBCw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 31 Mar 2026 13:50:21 +0300 Stepanov Anatoly wrote: > On 3/31/2026 1:46 PM, Stepanov Anatoly wrote: > > On 3/31/2026 4:31 AM, SeongJae Park wrote: > >> Hello Asier, > >> > >> On Mon, 30 Mar 2026 14:57:58 +0000 wrote: > >> > >>> From: Asier Gutierrez > >>> > >>> This patch set introces a new action: DAMOS_COLLAPSE. > >>> > >>> For DAMOS_HUGEPAGE and DAMOS_NOHUGEPAGE to work, khugepaged should be > >>> working, since it relies on hugepage_madvise to add a new slot. This > >>> slot should be picked up by khugepaged and eventually collapse (or > >>> not, if we are using DAMOS_NOHUGEPAGE) the pages. If THP is not > >>> enabled, khugepaged will not be working, and therefore no collapse > >>> will happen. > >> > >> I should raised this in a previous version, sorry. But, that is only a half of > >> the picture. That is, khugepaged is not the single THP allocator for > >> MADV_HUGEPAGE. IIUC, MADV_HUGEPAGE-applied region also allocates huge pages in > >> page fault time. According to the man page, > >> > >> The kernel will regularly scan the areas marked as huge page candidates > >> to replace them with huge pages. The kernel will also allocate huge pages > >> directly when the region is naturally aligned to the huge page size (see > >> posix_memalign(2)). > >> > > I think key difference between DAMOS_HUGEPAGE and DAMOS_COLLAPSE is the granularity. > > > > In DAMOS_HUGEPAGE case, the granularity is always VMA, even if the hot region is narrow. > > It's true for both page-fault based collapse and khugepaged collapse. > *page-fault THP allocation, not collapse of course. Good point. I think this difference can also help answering why DAMOS_COLLAPSE was making less huge pages in the test. > > > > > With DAMOS_COLLAPSE we can cover cases, when there's large VMA, for example, > > which contains some hot VA region inside, so we can collapse just that region, not the whole VMA. This also makes sense to me. Also I think this aligns to what we discussed for MADV_COLLAPSE intro. Thanks, SJ [...]