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From: Shakeel Butt To: "Barry Song (Xiaomi)" Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, david@kernel.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, chrisl@kernel.org, kasong@tencent.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, baoquan.he@linux.dev, youngjun.park@lge.com, jp.kobryn@linux.dev, usama.arif@linux.dev Subject: Re: [RFC PATCH 1/3] mm: avoid unnecessary lru drain for wp_can_reuse_anon_folio() Message-ID: References: <20260611105124.98668-1-baohua@kernel.org> <20260611105124.98668-2-baohua@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam07 X-Rspam-User: X-Stat-Signature: cbhbygj8kdz61qzy1kfwa84p4a738azw X-Rspamd-Queue-Id: 02ACE160014 X-HE-Tag: 1781201875-980600 X-HE-Meta: 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 sJDoTCDP FFqWy1Nm9QSZtqSkmyIH7PiF8vo+ow0Fsn00cyBjDhJ3Uk53+MD7JDfDuTea3fXxPkhtgmZiu7O6JOdcTl6a+g87OTkpOnQgjKbiqyr23X7bHmzLbLXl9kBFUZ3sI++imBVGELz5+6hGVysixVI4Mj8WcSDnr7FIOJtWNvsHpKERt+uAQqT2QUY1wGgYf1iU8tidGZVCqg4ON6YmfrVC/mTSymqBtlYm2xyMC0NXRQf8y39Zb7xlkmZFSKCASDiQmHGuyzb7i6pNQXnT5YnTlKmLgEg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Jun 11, 2026 at 11:09:43AM -0700, Shakeel Butt wrote: > On Thu, Jun 11, 2026 at 06:51:22PM +0800, Barry Song (Xiaomi) wrote: > > We always unconditionally drain the LRU before retrying anon folio > > reuse in wp_can_reuse_anon_folio(). Instead, assume !LRU anon folios > > are in lru_cache, and use the refcount to avoid many unnecessary LRU > > drains. > > > > Signed-off-by: Barry Song (Xiaomi) > > --- > > mm/memory.c | 8 +++++++- > > 1 file changed, 7 insertions(+), 1 deletion(-) > > > > diff --git a/mm/memory.c b/mm/memory.c > > index 56be920c56d7..487a34377a7b 100644 > > --- a/mm/memory.c > > +++ b/mm/memory.c > > @@ -4193,12 +4193,18 @@ static bool wp_can_reuse_anon_folio(struct folio *folio, > > */ > > if (folio_test_ksm(folio) || folio_ref_count(folio) > 3) > > return false; > > - if (!folio_test_lru(folio)) > > + if (!folio_test_lru(folio)) { > > + /* > > + * Assume folio is on lru_cache and holds a cache reference. > > + */ > > + if (folio_ref_count(folio) > 2 + folio_test_swapcache(folio)) > > + return false; > > In your experiments, how much amount of drains were reduced due to this specific > check? > > I wonder if that data can motivate to introduce lru_add_drain_folio(folio) which > only drains if the given folio is in the local lru_add cache. Actually if we can peek into lru_add cache and folio_ref_count(folio) is exactly equal to (2 + folio_test_swapcache(folio)) and folio is not on LRU then we can just reuse folio if it is in lru_add cache without draining, right? > > > /* > > * We cannot easily detect+handle references from > > * remote LRU caches or references to LRU folios. > > */ > > lru_add_drain(); > > + } > > if (folio_ref_count(folio) > 1 + folio_test_swapcache(folio)) > > return false; > > if (!folio_trylock(folio)) > > -- > > 2.39.3 (Apple Git-146) > >