lkml.org 
[lkml]   [2009]   [Jun]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: mmotm 2009-06-02-16-11 uploaded (readahead)
Date
> On Tue, 02 Jun 2009 20:54:39 -0700
> Randy Dunlap <randy.dunlap@oracle.com> wrote:
>
> > akpm@linux-foundation.org wrote:
> > > The mm-of-the-moment snapshot 2009-06-02-16-11 has been uploaded to
> > >
> > > http://userweb.kernel.org/~akpm/mmotm/
> > >
> > > and will soon be available at
> > >
> > > git://git.zen-sources.org/zen/mmotm.git
> >
> >
> > readahead-add-blk_run_backing_dev.patch:
> >
> > mm/readahead.c: In function 'page_cache_async_readahead':
> > mm/readahead.c:559: error: implicit declaration of function 'blk_run_backing_dev'
>
> hm, yeah, CONFIG_BLOCK=n.
>
> Doing a block-specific call from inside page_cache_async_readahead() is
> a bit of a layering violation - this may not be a block-backed
> filesystem at all.
>
> otoh, perhaps blk_run_backing_dev() is wrongly named and defined in the
> wrong place. Perhaps non-block-backed backing_devs want to implement
> an unplug-style function too? In which case the whole thing should be
> renamed and moved outside blkdev.h.
>
> If we don't want to do that, shouldn't backing_dev_info.unplug* be
> wrapped in #ifdef CONFIG_BLOCK? And wasn't it a layering violation to
> put block-specific things into the backing_dev_info?
>
> Jens, talk to me!
>
> From the readahead POV: does it make sense to call the backing-dev's
> "unplug" function even if that isn't a block-based device? Or was this
> just a weird block-device-only performance problem? Hard to say.

More problematic.

The patch comment says

+ /*
+ * Normally the current page is !uptodate and lock_page() will be
+ * immediately called to implicitly unplug the device. However this
+ * is not always true for RAID conifgurations, where data arrives
+ * not strictly in their submission order. In this case we need to
+ * explicitly kick off the IO.


However, hifumi-san's test result doesn't have IO reordering log.
At least the comment is wrong. and We still don't know why nobody can
reproduce his issue.






\
 
 \ /
  Last update: 2009-06-04 03:29    [W:0.056 / U:1.236 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site