Re: [PATCH][5/?] count writeback pages in nr_scanned

[Andrea Arcangeli]

On Wed, Jan 05, 2005 at 08:47:06PM -0800, Andrew Morton wrote:
> That's my point.  blk_congestion_wait() will always sleep, regardless of

Since I've no pending bugs at all with the mainline codebase I rate this
just a theoretical issue: but even sleeping for a fixed amount of time
is unreliable there, for example if the storage is very slow. That's why
using io_schedule_timeout for that isn't going to be a fix.

The fix is very simple and it is to call wait_on_page_writeback on one
of the pages under writeback. That guarantees some _writeback_ progress
has been made before retrying. That way some random direct-io or a too
short timeout, can't cause malfunction.
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