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Re: Mystery solved? files not written for days...

To: Eric Sandeen <sandeen@xxxxxxxxxxx>
Subject: Re: Mystery solved? files not written for days...
From: Felix Blyakher <felixb@xxxxxxx>
Date: Mon, 30 Mar 2009 17:30:54 -0500
Cc: xfs mailing list <xfs@xxxxxxxxxxx>
In-reply-to: <49D14120.8040804@xxxxxxxxxxx>
References: <49D14120.8040804@xxxxxxxxxxx>

On Mar 30, 2009, at 5:01 PM, Eric Sandeen wrote:


[PATCH] writeback: guard against jiffies wraparound on
inode->dirtied_when checks

The "jiffies wraparound" sounds very familiar, but I
thought it's been fixed ages ago.

When a file is continually dirtied, the check in sync_sb_inodes:

       /* Was this inode dirtied after sync_sb_inodes was called? */
       if (time_after(inode->dirtied_when, start))

may have large windows where this trips on the first
(continually-dirtied) inode on the list when the time_after check has
wrapped, causing the nothing to be written out for that superblock,
potentially for days.

Could this be the reason for those various "hey, my file disappeared
after a crash and I hadn't written to it for *days*" reports we got now
and then, leaving us all scratching our heads?

The "jiffies wraparound" could definitely cause this.



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