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b=DL41gg3hXNC/cq90W8a3nkPQ5S8npsYyl3Elz+j7FnAf1iArK02ZWOKrMEedVMUhz xZXAWWeuHXIW510rXC3MDxB3E+PnDuhUZsS7vTUD/XxT9CLcWUFUYiCX0cHFjzjj76 CmTIf2duTl5aOoydeXP1M/+MdlWv1YtQ8yoMggTbIWccFI4G4EtyncbGv9yafZBBP/ V918pMvHzgudeorImk7RjdvHeWnUDiZDGCc5EHqWap4wKAgpFH5n93uftOzY2srSAl cV3fJGpi0+YrDMO+5zb559pLfa0b5zLb52tgIOfWh39zP9sSr5JcJ4KjMAa4FltC9Z gGuxTfHBa8jMA== Message-ID: Date: Mon, 7 Sep 2026 16:30:28 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/2] mm/huge_memory: dequeue the deferred split after the split freeze To: Kiryl Shutsemau Cc: akpm@linux-foundation.org, ljs@kernel.org, hannes@cmpxchg.org, usama.arif@linux.dev, lance.yang@linux.dev, ziy@nvidia.com, kasong@tencent.com, hughd@google.com, baolin.wang@linux.alibaba.com, baohua@kernel.org, liam@infradead.org, nico.pache@linux.dev, dev.jain@arm.com, ryan.roberts@arm.com, balbirs@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260831091514.1879786-1-kirill@shutemov.name> <20260831091514.1879786-3-kirill@shutemov.name> 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: rspam11 X-Rspam-User: X-Stat-Signature: 9woh9magkqds6dufkijj1kjnxuimqryi X-Rspamd-Queue-Id: 4C22140003 X-HE-Tag: 1788791437-610 X-HE-Meta: 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 s2+bUTZ8 o/g2r5vzPj7A2JCzqchP89PuQbghuCJfcOm5r+jCUp6R/q+CFngt51DrIcIhk507jXyycHqlLo44iV/I8BFdQi212TeLDekhr3KeQHqRhx5aculAh2zs5jcXOUk8I/xwcazvZ72dz5ZBLHPWrPfqPBPRfl8imF5uZ+QYnFhfCQgXWyl9XBCOigvrxjdH41COioJOCkqbtSeUIkY0WjGQWLqBFsa6wXIYmLoHtmKmDW97QJKW6PNXK2X3oCdMOcLFoooCnuGGKbChB32dQIBkhpBiPS4naLBzKNDfq1YbaysANs2mBgDDFBAgL5DEdLDt5lzdqDwxOvg+8QAZ2t9I1xulHpfzhZU0iaVMB1x0zOchxL5y8FpPi1xavX02YChdhLwzKB1SU0Q6xVMtLM7UZpRbgQRD8UC8DH6QK Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/7/26 16:12, Kiryl Shutsemau wrote: > On Mon, Sep 07, 2026 at 03:55:53PM +0200, David Hildenbrand (Arm) wrote: >> On 8/31/26 11:15, Kiryl Shutsemau wrote: >>> From: "Kiryl Shutsemau (Meta)" >>> >>> __folio_freeze_and_split_unmapped() takes the deferred split list_lru lock >>> across the freeze. It is only there to stop deferred_split_scan() from >>> touching the folio under split. >>> >>> With deferred_split_isolate() fixed, the workaround can be dropped. >>> >>> Unqueue the folio after folio_ref_freeze(), the way >>> __folio_migrate_mapping() does: folio_unqueue_deferred_split() needs a >>> zero refcount and a memcg still set, and both hold there. >>> >>> If the split is called from deferred_split_scan(), the unqueue is a >>> no-op -- the folio is already removed from the list. But >>> PG_partially_mapped is still set, so it has to be cleared here or >>> MTHP_STAT_NR_ANON_PARTIALLY_MAPPED never comes back down. >>> >>> Assisted-by: Claude-Code:claude-opus-5 >>> Signed-off-by: Kiryl Shutsemau (Meta) >>> Reviewed-by: Zi Yan >>> Reviewed-by: Johannes Weiner >>> Acked-by: David Hildenbrand (Arm) >>> --- >>> mm/huge_memory.c | 44 +++++++++++++------------------------------- >>> 1 file changed, 13 insertions(+), 31 deletions(-) >>> >>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>> index 6281ed993243..c84e8cbc986d 100644 >>> --- a/mm/huge_memory.c >>> +++ b/mm/huge_memory.c >>> @@ -3931,41 +3931,27 @@ static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int n >>> struct folio *end_folio = folio_next(folio); >>> struct folio *new_folio, *next; >>> int old_order = folio_order(folio); >>> - struct list_lru_one *lru; >>> - bool dequeue_deferred; >>> int ret = 0; >>> >>> VM_WARN_ON_ONCE(!mapping && end); >>> - /* >>> - * If this folio can be on the deferred split queue, lock out >>> - * the shrinker before freezing the ref. If the shrinker sees >>> - * a 0-ref folio, it assumes it beat folio_put() to the list >>> - * lock and must clean up the LRU state - the same dequeue we >>> - * will do below as part of the split. >>> - */ >>> - dequeue_deferred = folio_test_anon(folio) && old_order > 1; >>> - if (dequeue_deferred) { >>> - struct mem_cgroup *memcg; >>> >>> - rcu_read_lock(); >>> - memcg = folio_memcg(folio); >>> - lru = list_lru_lock(&deferred_split_lru, >>> - folio_nid(folio), &memcg); >>> - } >> >> Nice cleanup. >> >>> if (folio_ref_freeze(folio, folio_cache_ref_count(folio) + 1)) { >>> struct swap_cluster_info *ci = NULL; >>> struct lruvec *lruvec; >>> >>> - if (dequeue_deferred) { >>> - __list_lru_del(&deferred_split_lru, lru, >>> - &folio->_deferred_list, folio_nid(folio)); >>> - if (folio_test_partially_mapped(folio)) { >>> - folio_clear_partially_mapped(folio); >>> - mod_mthp_stat(old_order, >>> - MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1); >>> - } >>> - list_lru_unlock(lru); >>> - rcu_read_unlock(); >>> + /* Take off the deferred split queue while frozen and memcg set */ >>> + folio_unqueue_deferred_split(folio); >>> + >>> + /* >>> + * deferred_split_scan() takes the folio off the queue before it >>> + * splits it, so the unqueue above finds an empty list and >>> + * leaves PG_partially_mapped set. >>> + * Clear it here: the flag does not survive the split. >>> + */ >>> + if (folio_test_partially_mapped(folio)) { >>> + folio_clear_partially_mapped(folio); >>> + mod_mthp_stat(old_order, >>> + MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1); >>> } >> >> In general, >> >> Acked-by: David Hildenbrand (Arm) >> >> But I do wonder whether this sequence (that also >> __folio_unqueue_deferred_split()) performs would deserve a small local helper in >> mm/huge_memory.c >> >> Could be done as a separate cleanup. > > Just to be sure, do you want a helper like this: Something like that. I'd probably call it folio_reset_partially_mapped() -- Cheers, David