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Date:   Fri, 24 May 2019 12:52:13 -0400
From:   "Theodore Ts'o" <tytso@mit.edu>
To:     Sahitya Tummala <stummala@codeaurora.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Kirill Tkhai <ktkhai@virtuozzo.com>,
        Michal Hocko <mhocko@suse.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Yafang Shao <laoar.shao@gmail.com>,
        Roman Gushchin <guro@fb.com>,
        Mel Gorman <mgorman@techsingularity.net>, linux-mm@kvack.org,
        Jaegeuk Kim <jaegeuk@kernel.org>,
        Eric Biggers <ebiggers@kernel.org>,
        linux-fscrypt@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/vmscan.c: drop all inode/dentry cache from LRU
Message-ID: <20190524165213.GB2765@mit.edu>
Mail-Followup-To: Theodore Ts'o <tytso@mit.edu>,
        Sahitya Tummala <stummala@codeaurora.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Kirill Tkhai <ktkhai@virtuozzo.com>, Michal Hocko <mhocko@suse.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Yafang Shao <laoar.shao@gmail.com>, Roman Gushchin <guro@fb.com>,
        Mel Gorman <mgorman@techsingularity.net>, linux-mm@kvack.org,
        Jaegeuk Kim <jaegeuk@kernel.org>,
        Eric Biggers <ebiggers@kernel.org>, linux-fscrypt@vger.kernel.org,
        linux-kernel@vger.kernel.org
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On Fri, May 24, 2019 at 01:36:01PM +0530, Sahitya Tummala wrote:
> This is important for the scenario where FBE (file based encryption)
> is enabled. With FBE, the encryption context needed to en/decrypt a file
> will be stored in inode and any inode that is left in the cache after
> drop_caches is done will be a problem. For ex, in Android, drop_caches
> will be used when switching work profiles.
> 
> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>

Instead of making a change to vmscan.c, it's probably better to
migrate to the new fscrypt key-management framework, which solves this
problem with an explicit FS_IOC_REMOVE_ENCRYPTION_KEY ioctl.  This
allows the system to remove all inodes that were made available via a
single key without having nuking all other inodes --- this would make
it much faster after a user logs out of ChromeOS, for example:

See:

	https://patchwork.kernel.org/patch/10952019/

							- Ted