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b=gI8ftB0YMB5vFgdTJ/VqSy11B4Hgym+5tR+cWMB1A5tmkqCbZ/XV45UeEkAae5CQp ThqtR5Ty7VZZyVLE+VWPHUJ06pm2305BGgyL5gsuJo79cG+78PL8Nn2/Kq0BFXEbtx ZCnozSOxaLCXytDG5G4qd0K+rIk7GVTlL/GtgC8NlNJOnijP94SSajKkEqwDWvBzxT DyB8P/UTClwDwgCX8ReGWUGXZQCKn3zJ7wvxVf4QulqIGQDxC3I4+DnWtAeUmZQpOB qVTZNLTV8kDg8HIQV09OZ7gOxF1epLwiTS1PLIVCJKHKh3lWeYBZnPb1G4u4arAAkw GfbSDawgyVYKA== Message-ID: Date: Mon, 7 Sep 2026 15:55:53 +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 , akpm@linux-foundation.org, ljs@kernel.org, hannes@cmpxchg.org, usama.arif@linux.dev Cc: 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, kas@kernel.org, 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-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 4538F40004 X-Stat-Signature: prymw9unfeom8uxgethaho936wsxdwb5 X-HE-Tag: 1788789360-880987 X-HE-Meta: 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 VSKw2cqt n6/Q33+gEem/xyFuEsw/H7YVeCXnDougHfoAIFhvvrc0ZONgYpqOvsotduow9ab0KrOlhgzZH+1qkROjU1nkO8NkKrFENU9I4BChztL6NCVO8/TYktdp+9/N2lrcQe/Y6UEB+dm7bBIojQwlAuaJ8adZrSuTPNWuaKgQshHtr9Lh/bJqbd3SezBUTtcrbZToMM/AaFlVMxYeRv4ak66qT8kx7FklNBwLxZia2SMKd3STvmI9oT3En1JSGeO9dNGOQzSHlef9smIF+wTL1Y3kuKBiUrL14NPK0/iEFhVdbF9Osnizs0tm3RMzn3juamcAMoyIYtUL5yMTe3ineaYqXOTuZnD7t5FjtndcojfvkfNxE8LH9AUgXXV80fpVAovA1Amj0lDNdKhcS0RcWnN9nx2/yTEB8m8HLBKOq Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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. -- Cheers, David