Re: [RESEND][PATCH v2] block: remove plugging at buffered writetime

From: Andrew Morton
Date: Wed Apr 11 2012 - 19:13:42 EST


On Mon, 09 Apr 2012 10:34:44 -0400
Jeff Moyer <jmoyer@xxxxxxxxxx> wrote:

> Wu Fengguang <fengguang.wu@xxxxxxxxx> writes:
>
> > Buffered write(2) is not directly tied to IO, so it's not suitable to
> > handle plug in generic_file_aio_write().
> [snip, moved]
> > Note that plugging for O_SYNC writes is also removed. The user may pass
> > arbitrary @size arguments, which may be much larger than the preferable
> > I/O size, or may cross extent/device boundaries. Let the lower layers
> > handle the plugging. Otherwise the plugging code here will turn the
> > low level plugging into no-ops.
>
> I assume you have some numbers to back this up, right? Care to share
> those?

Yes please.

We've broken this stuff a few times recently - we should review and
test carefully.

> > Also moves unplugging for direct I/O from around ->direct_IO() down to
> > do_blockdev_direct_IO().
>
> This could be handled in a separate patch.

I think that would be better.
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