From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Minchan Kim <minchan@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Tino Lehnig <tino.lehnig@contabo.de>,
stable@vger.kernel.org, Jens Axboe <axboe@kernel.dk>
Subject: Re: [PATCH 1/2] zram: remove BD_CAP_SYNCHRONOUS_IO with writeback feature
Date: Fri, 3 Aug 2018 11:39:29 +0900 [thread overview]
Message-ID: <20180803023929.GA7500@jagdpanzerIV> (raw)
In-Reply-To: <20180802141304.d0589ddc5f8213429ab3b565@linux-foundation.org>
On (08/02/18 14:13), Andrew Morton wrote:
[..]
> That changelog is rather hard to follow. Please review my edits:
>
> : If zram supports writeback feature, it's no longer a BD_CAP_SYNCHRONOUS_IO
^BDI_CAP_SYNCHRONOUS_IO
[..]
> A reader looking at this would wonder "why the heck are we doing that".
> Adding a code comment would help them.
The interesting thing here is that include/linux/backing-dev.h
BDI_CAP_SYNCHRONOUS_IO comment says
"Device is so fast that asynchronous IO would be inefficient."
Which is not the reason why BDI_CAP_SYNCHRONOUS_IO is used by ZRAM.
Probably, the comment needs to be updated as well.
Both SWP_SYNCHRONOUS_IO and BDI_CAP_SYNCHRONOUS_IO tend to pivot
"efficiency" [looking at the comments], but in ZRAM's case the whole
reason to use SYNC IO is a race condition and user-after-free that
follows.
-ss
next prev parent reply other threads:[~2018-08-03 2:36 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-02 5:11 [PATCH 1/2] zram: remove BD_CAP_SYNCHRONOUS_IO with writeback feature Minchan Kim
2018-08-02 21:13 ` Andrew Morton
2018-08-03 2:39 ` Sergey Senozhatsky [this message]
2018-08-03 2:52 ` Sergey Senozhatsky
2018-08-03 3:00 ` Minchan Kim
2018-08-03 4:13 ` Sergey Senozhatsky
2018-08-03 4:51 ` Minchan Kim
2018-08-03 5:23 ` Sergey Senozhatsky
2018-08-03 5:45 ` Sergey Senozhatsky
2018-08-03 2:51 ` Minchan Kim
2018-08-03 23:28 ` Andrew Morton
2018-08-05 23:15 ` Minchan Kim
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