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From: Shakeel Butt To: Barry Song 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=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 0A9CF20003 X-Stat-Signature: daf1uukzbf36fzi6gt58zii1bygurw6w X-HE-Tag: 1781708924-710322 X-HE-Meta: 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 3Q26sAz5 Y0vlFhsf3C4Vc/pHQcfzsbBb1HG9nmJukhRqH/aHYj41FrCLNS+/APOLW5/6ZRgSoV4AycyIn0X2CsbJej/R7LYIniVtlHbYrXLetq1D+Y+Wx5hSpXgAGSjFv2iv0SfANr7cTPYYnugz0/kiR6V4wpZ47aEpUbk3unFr4eLg4s2KNeRjWePqrzIM4yQvEKHOTd2V2uFPG24GMz2wIR1YjnIPH/MboYylwOAPdFKugBeTUoaFsi4vGOy+fGIlm7DeW8wW/KQuzmLFTsZrCjl6azBqXP48sSjeUBcdhehQ33dVOb6WTygL1CgoYHw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Jun 12, 2026 at 12:48:19PM +0800, Barry Song wrote: > On Fri, Jun 12, 2026 at 2:10 AM 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? > > This is a very good question. I booted the system into Ubuntu, and after > boot completed I observed: > > wp_reuse_skipped_drain: 5542 > do_swap_skipped_drain: 0 > > Then I built the kernel in a 1GB memcg using zRAM swap, and observed: > > wp_reuse_skipped_drain: 25017 > do_swap_skipped_drain: 43595 > > So in summary, even without swap-in we can save a significant number of > drains in wp_can_reuse_anon_folio(). With heavy swap-in workloads, most > of the savings come from avoiding drains in do_swap_page(), while we > still see a substantial number of skipped drains in wp_can_reuse_anon_folio(). Thanks and this is very good info. Add this in the commit message when you send the non-RFC version.