From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CA3B04EE877 for ; Mon, 7 Sep 2026 13:55:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788789361; cv=none; b=o9xEsQtjAVV7qpczDe3Gh1D3bfp0gfpDcgvJXCdJ6qtF9YiFx8xRt9OFVbX/KIbSN79BFwwWZ6WF0VyN8+t8TDAR7DYprQAKSuQQ4nfIJQpoD1V6aJ0z73YpSVNngqhNGIDvWjt3lXQIk2ift9XJfGUUqPN0qjCsPDZfNkbz/tY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788789361; c=relaxed/simple; bh=OnJ7HC00/rddbJsQSNNRG2i/15vqOfuKoPk7IGJ5hHc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=pauBeYFEvDaMHFg8jD65BcEjcn51V+WQ3fd0z0flHIJCUIvZ98jTuu9ERG0ZaISwPQ25Eoqbs2Ya4il19UWyo9d1iMriRl01KHB8sWEifez6GaqRH1cd92Ecbffvfe0hTbJqBvtpC9aZcZHToDiRVO2+zmxGe3AS/rY0uS2BugY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=gI8ftB0Y; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="gI8ftB0Y" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2C5841F00A3A; Mon, 7 Sep 2026 13:55:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788789359; bh=EZB4SZnhJn7B8NJkES4V3S9ML1xc3yKh26KW0DCPkAI=; h=Date:Subject:To:Cc:References:From:In-Reply-To; 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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