Re: [PATCH 11/12] vmscan: Write out dirty pages in batch

From: Christoph Hellwig
Date: Tue Jun 15 2010 - 07:01:14 EST

On Mon, Jun 14, 2010 at 09:16:29PM -0400, Rik van Riel wrote:
> >Besides, there really isn't the right context in the block layer to
> >be able to queue and prioritise large amounts of IO without
> >significant penalties to some higher layer operation.
> Can we kick flushing for the whole inode at once from
> vmscan.c?

kswapd really should be a last effort tool to clean filesystem pages.
If it does enough I/O for this to matter significantly we need to
fix the VM to move more work to the flusher threads instead of trying
to fix kswapd.

> Would it be hard to add a "please flush this file"
> way to call the filesystem flushing threads?

We already have that API, in Jens' latest tree that's
sync_inodes_sb/writeback_inodes_sb. We could also add a non-waiting
variant if required, but I think the big problem with kswapd is that
we want to wait on I/O completion under circumstances.
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