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d=linux-foundation.org; s=korg; t=1688494020; bh=ax5aSQO7Q8i6scQMJDEtYLdG7HxPbixeLmpQBL1NGoo=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=LiSYfNW4TUnYtrQLCm6LWhvyq7sD/au+ZwfSvS7XN04La/WLKynldo0dtKtmTTBwL WunDie3WP/NVO2OTkEben6uoo40mXyy3iL4tIc0/SXP+KDsfcah/LL3k2H6Nid4f1F iT9+PXkbHIQqe5sPUk5oPnCMOivXMUqefaaSpfF8= Date: Tue, 4 Jul 2023 11:06:59 -0700 From: Andrew Morton To: Andrew Yang Cc: Alexander Viro , Christian Brauner , Matthias Brugger , AngeloGioacchino Del Regno , , , , , , , linux-mm@kvack.org Subject: Re: [PATCH] fs: drop_caches: draining pages before dropping caches Message-Id: <20230704110659.3e1de8001f9208e7278352e8@linux-foundation.org> In-Reply-To: <20230630092203.16080-1-andrew.yang@mediatek.com> References: <20230630092203.16080-1-andrew.yang@mediatek.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 69EE51C0027 X-Rspam-User: X-Stat-Signature: ine1zp5fu6tqtehhbye8tah586c94aub X-Rspamd-Server: rspam01 X-HE-Tag: 1688494022-494768 X-HE-Meta: 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 Sbv5stDs 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, 30 Jun 2023 17:22:02 +0800 Andrew Yang wrote: > We expect a file page access after dropping caches should be a major > fault, but sometimes it's still a minor fault. That's because a file > page can't be dropped if it's in a per-cpu pagevec. Draining all pages > from per-cpu pagevec to lru list before trying to drop caches. > > --- a/fs/drop_caches.c > +++ b/fs/drop_caches.c > @@ -10,6 +10,7 @@ > #include > #include > #include > +#include > #include "internal.h" > > /* A global variable is a bit ugly, but it keeps the code simple */ > @@ -59,6 +60,7 @@ int drop_caches_sysctl_handler(struct ctl_table *table, int write, > static int stfu; > > if (sysctl_drop_caches & 1) { > + lru_add_drain_all(); > iterate_supers(drop_pagecache_sb, NULL); > count_vm_event(DROP_PAGECACHE); > } um, yes. I'm suprised that this oversight has survived 20+ years.