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b=QEIm92HTankRnWAoOl3s0CVEUmiBcSwE+/rA1U8WIrhMSiJa7A9uYtSOOyQAxllAH 23/lI509xvayAf1RjWg9a9ANlH/YK3W07wl/JbQSHydjl4VbQ/HtPks+hfQrHcil/c l9vbYojjqtvD52h48V3D10AuKdx+O0PJx8plH3XSkRUxxPQ8B0q0Ut4H49rBKcfE5U GMvMyMDsSBvfTdglAESpRIp0W8hwci1y99wuEWIBbVLOm8prwITIDgmnw9sVxkuW3n ilrWuLXZMOWI6GyVaBEai63svLfEXVbSWeGMd6CX5R+Uvy1cCQuSoRU9yE0Eq5x7zR k35q+gYWDsBGQ== Message-ID: <716c7351-2641-4317-8675-e07a16a1efe2@kernel.org> Date: Tue, 2 Jun 2026 14:11:16 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/1] mm/thp: clear deferred split shrinker bits when queues drain To: Lance Yang , akpm@linux-foundation.org, hannes@cmpxchg.org Cc: ljs@kernel.org, shakeel.butt@linux.dev, mhocko@kernel.org, david@fromorbit.com, roman.gushchin@linux.dev, muchun.song@linux.dev, qi.zheng@linux.dev, yosry.ahmed@linux.dev, ziy@nvidia.com, liam@infradead.org, usama.arif@linux.dev, kas@kernel.org, vbabka@kernel.org, ryncsn@gmail.com, zaslonko@linux.ibm.com, gor@linux.ibm.com, wangkefeng.wang@huawei.com, baolin.wang@linux.alibaba.com, baohua@kernel.org, dev.jain@arm.com, npache@redhat.com, ryan.roberts@arm.com, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260602043453.67597-1-lance.yang@linux.dev> <1dce1561-b42a-4322-a99f-89eba1e7c227@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 9923340009 X-Stat-Signature: 9zh69uxk6j649p9nzzm68rpx9r6tmidj X-HE-Tag: 1780402284-993244 X-HE-Meta: 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 tLGuftUM JudaWUk+yO9Zje22ndz8ZhnrIsdFCy0hdy+pBM94M0M0DMWHT9UTZyIf+jEPYdqSdJcT0P38NYo0YOjVVd9mTuv+Wo1TIpuVyWIUeZdgYmsG3LwVd3vWL2dM/whERX/wc3WDH5Bmlc8fVg2BuRlish3fW+lPyRzSxmBwrg/VX7//S0QHtMI84B5ptVRi5p/xZmG07/2hKafojlJj3vJD+4CULBWUWiSSMh3JW5e0o8xW3VxibxTA99BU3EpvpeYkuG8g6tWlBXuGef1ZQ2MpNTUYPgaMvbeaYW4Bn Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/2/26 06:38, Lance Yang wrote: > Sorry, I missed Johannes in Cc ... > > On 2026/6/2 12:34, Lance Yang wrote: >> From: Lance Yang >> >> deferred_split_count() returns the raw list_lru count. When the per-memcg, >> per-node list is empty, that count is 0. >> >> That skips scanning, but it does not tell memcg reclaim that the shrinker >> is empty. shrink_slab_memcg() only clears the memcg shrinker bit when the >> count callback reports SHRINK_EMPTY. What's the effect of that? Would we consider it a fix that we'd want to backport? >> >> Return SHRINK_EMPTY for an empty deferred split list, so the bit can be >> cleared once the queue has drained. >> >> Signed-off-by: Lance Yang >> --- >>   mm/huge_memory.c | 5 ++++- >>   1 file changed, 4 insertions(+), 1 deletion(-) >> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index 72f6caf0fec6..62d598290c3b 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -4397,7 +4397,10 @@ void deferred_split_folio(struct folio *folio, bool >> partially_mapped) >>   static unsigned long deferred_split_count(struct shrinker *shrink, >>           struct shrink_control *sc) >>   { >> -    return list_lru_shrink_count(&deferred_split_lru, sc); >> +    unsigned long count; >> + >> +    count = list_lru_shrink_count(&deferred_split_lru, sc); >> +    return count ?: SHRINK_EMPTY; >>   } >>     static bool thp_underused(struct folio *folio) > This is against Johannes' work, right? If this is a fix, likely it would be fixing 87eaceb3faa5 ("mm: thp: make deferred split shrinker memcg aware"), right? -- Cheers, David