Re: [PATCH 2.6.3-mm4] writeback trylock patch

[Andrew Morton]

Daniel McNeil <daniel@xxxxxxxx> wrote:
>
> Here is update to the wb_rwsema patch that adds back the trylock.
> It avoids the hang hugh was seeing by setting encountered_congestion
> if the trylock fails and checking it in sync_sb_inodes().  Hugh
> tested this and did not see the hang.
> 
> This prevents non-sync writebacks to from blocking behind sync
> writebacks.
> 
> This patch applies to 2.6.4-rc1-mm2.
> 
> Thoguhts?

spose so.  One concern is with writer throttling: if the caller of write(2)
is simply skipping a large file then it should throttle in
balance_dirty_pages() or block on i_sem I guess.  This code is getting
pretty sticky.

Why are you setting wbc->encountered_congestion in sync_sb_inodes()?

And why are you doing a trylock in __filemap_fdatawrite()?  That only
affects fadvise(), and probably we want to block in there anyway.  It
doesn't matter really but less code is better code.


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