linux-kernel - Re: [PATCH] Fix queueing work if !bdi_cap_writeback

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Message-ID: <87ehm4n28u.fsf@devron.myhome.or.jp>
Date:	Fri, 14 Sep 2012 22:49:21 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Fengguang Wu <fengguang.wu@...el.com>
Cc:	viro@...iv.linux.org.uk, jack@...e.cz, hch@....de,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix queueing work if !bdi_cap_writeback_dirty()

Fengguang Wu <fengguang.wu@...el.com> writes:

>> > And BDI_CAP_NO_WRITEBACK is expected to be a static/constant flag that
>> > always evaluate to true/false for a given bdi.  There will be
>> > correctness problems if you change the BDI_CAP_NO_WRITEBACK flag
>> > dynamically.
>> 
>> I'm going to use it as static or per-sb by initialized in
>> fill_super(). And it uses always BDI_CAP_NO_WRITEBACK if sb is
>> available. Because own FS task flush instead.
>
> Ah OK, sorry I didn't quite catch your use case.
>
> But then if you set BDI_CAP_NO_WRITEBACK in the beginning, how come
> __bdi_start_writeback() will be called at all?

If we call mark_inode_dirty(inode), inode goes into bdi->wb.b_dirty.
And sync(2) calls __bdi_start_writeback() for all of bdi if bdi->wb.b_*
is not empty.

Thanks.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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