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

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Message-ID: <878vccmygy.fsf@devron.myhome.or.jp>
Date:	Sat, 15 Sep 2012 00:10:53 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Jan Kara <jack@...e.cz>
Cc:	Fengguang Wu <fengguang.wu@...el.com>, viro@...iv.linux.org.uk,
	hch@....de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix queueing work if !bdi_cap_writeback_dirty()

Jan Kara <jack@...e.cz> writes:

>> If flusher is working, it clears dirty flags of inode. But if those
>> handers can't flush at the time, we have to do redirty or something to
>> prevent the reclaim.
>   Well, if this is your only problem then I'd see better options than just
> disabling flusher thread. If the inability to write inode is rare, then
> redirtying seems like a reasonable option (despite I agree it's a bit
> ugly). If the inability to write is common, then you'll probably have to do
> the dirty inode tracking yourself in some list and expose inodes to VM when
> they are ready to be written. Or you handle writing of inodes yourself but
> leave writing of pages on flusher thread...

Basically all data can be data-integrity write like data logging, so it
would be more than common. And ->writepages() will also ignore WBC_SYNC_NONE.

> Because when you disable flusher thread completely you have to put all the
> smarts to avoid livelocks, keep fairness among processes, write old data,
> keep number of dirty pages under control into your filesystem which leads
> to a lot of duplication.

I'm not sure what you meant though. What is the difference with ignoring
WBC_SYNC_NONE?

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