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b=XhZ5wam45rznxZvw7gY0USWzU5QfUteHzSBCzZuoFfeYk9fbKGpP9JXYTo98LVWam MrTz64bB56Ez7PKLsdETUlpWEgebzZSfIqBuaPZOfOhLZUfNm0GTJIAN45voZE/EYO qeZ8OGp6AoTHEXKtruHinJg/0mqNn3ZzoVMFtZlR4eHbJtqGH5G6f6wHvAK0gzKN5m 9pPQfk69bty/aN0rZLbkTU8alwYp0cZ7i4K1zB7UhIrdU8XFKpXyRsjm3mbPhk21/x mOr2sQMdPWtu81RTdp57gduttlFviMNglvv1a7X7/8kc2L9pn3jXv61OcSOLwy6MVL u1GJv1xza3SFw== Message-ID: <584098de-dd48-4004-8e7e-3d826e60c860@kernel.org> Date: Wed, 8 Jul 2026 09:56:27 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 2/2] mm/memory: add anonymous mTHP folios to deferred split list To: Joanne Koong , akpm@linux-foundation.org, ljs@kernel.org Cc: usama.arif@linux.dev, 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, baohua@kernel.org, lance.yang@linux.dev, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, willy@infradead.org, linux-mm@kvack.org References: <20260707201735.4113107-1-joannelkoong@gmail.com> <20260707201735.4113107-3-joannelkoong@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 74FCFC0007 X-Stat-Signature: hjzfemtyh6hk4n6m5jdxwbh8uham3wow X-Rspam-User: X-HE-Tag: 1783497396-411329 X-HE-Meta: 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 qu+bAwmL Oj4FET2f/mHI7vRZrZJk+1PI408LnU1uSOrsxp1bhq85mGvNQLfQwPz/RjEqHgBL4aqFqEWdw32L5lsaOdbzogU/cR+wJ4HzXOiasfrlB27aXBjSbZ8dJyAL8fCaFVDQZPqj5pFHmWVx7PmY8cpSy3+RQ064IJxrEBe7zP6SvK+vXiC6ekbfKc7C3SdxrYsk7pfXDYPMOJuDw55VGo+0lmd7N/gijN5We0CNIFLTeOAOaBK7NHGTaaa55HtqNlzt1rA2l18XKPa10ch2zroHF+1mYBJZLMDU2Qs/fWk9uowBD5x9ddQaHJwUd9w== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/7/26 22:17, Joanne Koong wrote: > Unlike for PMD-sized folios, an anonymous mTHP folio doesn't get added > to the deferred split list at fault or collapse time. As a result, a > fully mapped mTHP folio that is mostly zero-filled doesn't get split by > the deferred split shrinker when the system is under memory pressure. > > Add anonymous mTHP folios to the deferred split list so that if there's > memory pressure, a zero-filled mTHP can be split with its zero pages > remapped to the shared zero page and then reclaimed. > > To minimize overhead on the common order-0 fault path, the > deferred_split_folio() call is guarded by an inline folio_test_large() > check. > > Suggested-by: Usama Arif > Signed-off-by: Joanne Koong > --- > mm/memory.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/memory.c b/mm/memory.c > index 6637c5b13c9b..441d918e3dc0 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -5259,6 +5259,8 @@ void map_anon_folio_pte_nopf(struct folio *folio, pte_t *pte, > folio_add_lru_vma(folio, vma); > set_ptes(vma->vm_mm, addr, pte, entry, nr_pages); > update_mmu_cache_range(NULL, vma, addr, pte, nr_pages); > + if (folio_test_large(folio)) > + deferred_split_folio(folio, false); > } > > static void map_anon_folio_pte_pf(struct folio *folio, pte_t *pte, I had a session [1] at LSF/MM about having essentially all large anon folios part of the the deferred split queue. (1) I don't think this scales. (2) I suspect the shrinker should make smarter decisions of what to scan/reclaim first. I think this needs more proper thought. [1] https://docs.google.com/presentation/d/1RfKWCY1AMVns-WLn-QdAWbI2a-rA7fbFyh7XD1Wn5BY/edit?usp=sharing -- Cheers, David