On Thu, May 29, 2014 at 6:58 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote:
>
> If the patch I sent solves the swap stack usage issue, then perhaps
> we should look towards adding "blk_plug_start_async()" to pass such
> hints to the plug flushing. I'd want to use the same behaviour in
> __xfs_buf_delwri_submit() for bulk metadata writeback in XFS, and
> probably also in mpage_writepages() for bulk data writeback in
> WB_SYNC_NONE context...
Yeah, adding a flag to the plug about what kind of plug it is does
sound quite reasonable. It already has that "magic" field, it could
easily be extended to have a "async" vs "sync" bit to it..
Of course, it's also possible that the unplugging code could just look
at the actual requests that are plugged to determine that, and maybe
we wouldn't even need to mark things specially. I don't think we ever
end up mixing reads and writes under the same plug, so "first request
is a write" is probably a good approximation for "async".
Linus
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