linux-kernel - Re: [PATCH 1/2] zram: remove BD_CAP_SYNCHRONOUS

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Message-Id: <20180803162818.8c4719232d6dfece21ebea30@linux-foundation.org>
Date:   Fri, 3 Aug 2018 16:28:18 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Tino Lehnig <tino.lehnig@...tabo.de>, stable@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH 1/2] zram: remove BD_CAP_SYNCHRONOUS_IO with writeback
 feature

On Fri, 3 Aug 2018 11:51:43 +0900 Minchan Kim <minchan@...nel.org> wrote:

> > Is it legitimate to be altering the bdi capabilities at this level?  Or
> > is this hacky?
> 
> Most of device's bdi capability seems to be static but there are few drivers
> which can change capability. For example, BDI_CAP_STABLE_WRITES
> 
> drivers/scsi/iscsi_tcp.c
> drivers/md/raid5.c
> 
> I believe it's driver itself advertisement stuff so I hope it's not hack.

The bdi is per-disk (per-queue).  So if zram changes the bdi for a
particular partition then it is accidentally mucking with the other
partitions as well, and it shouldn't do that.  At least, I think that's
how it works - it's been a while.  Jens, wake up ;)