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

[Rik van Riel <riel@redhat.com>]

On 06/15/2010 07:01 AM, Christoph Hellwig wrote:
> 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.

However, kswapd does not need to wait on I/O completion of
any page in particular - it just wants to wait on I/O
completion of any inactive pages in the zone (or memcg)
where memory is being freed.

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