* [BLOCK] phys_contig implies hw_contig
@ 2003-11-01 2:31 Herbert Xu
2003-11-02 4:45 ` David S. Miller
0 siblings, 1 reply; 5+ messages in thread
From: Herbert Xu @ 2003-11-01 2:31 UTC (permalink / raw)
To: axboe, Linux Kernel Mailing List
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Hi:
In ll_merge_requests_fn, it is checking blk_hw_contig_segments even if
blk_phys_contig_segments succeeds. This means that it may cause two
physically contiguous segments to be separated because the hw check
fails.
This patch fixes that.
Cheers,
--
Debian GNU/Linux 3.0 is out! ( http://www.debian.org/ )
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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Index: kernel-source-2.5/drivers/block/ll_rw_blk.c
===================================================================
RCS file: /home/gondolin/herbert/src/CVS/debian/kernel-source-2.5/drivers/block/ll_rw_blk.c,v
retrieving revision 1.9
diff -u -r1.9 ll_rw_blk.c
--- kernel-source-2.5/drivers/block/ll_rw_blk.c 11 Oct 2003 06:29:20 -0000 1.9
+++ kernel-source-2.5/drivers/block/ll_rw_blk.c 1 Nov 2003 02:24:52 -0000
@@ -1046,16 +1046,16 @@
return 0;
total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
- if (blk_phys_contig_segment(q, req->biotail, next->bio))
+ total_hw_segments = req->nr_hw_segments + next->nr_hw_segments;
+
+ if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
total_phys_segments--;
+ total_hw_segments--;
+ } else if (blk_hw_contig_segment(q, req->biotail, next->bio))
+ total_hw_segments--;
if (total_phys_segments > q->max_phys_segments)
return 0;
-
- total_hw_segments = req->nr_hw_segments + next->nr_hw_segments;
- if (blk_hw_contig_segment(q, req->biotail, next->bio))
- total_hw_segments--;
-
if (total_hw_segments > q->max_hw_segments)
return 0;
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [BLOCK] phys_contig implies hw_contig
2003-11-01 2:31 [BLOCK] phys_contig implies hw_contig Herbert Xu
@ 2003-11-02 4:45 ` David S. Miller
2003-11-02 4:47 ` Herbert Xu
0 siblings, 1 reply; 5+ messages in thread
From: David S. Miller @ 2003-11-02 4:45 UTC (permalink / raw)
To: Herbert Xu; +Cc: axboe, linux-kernel
On Sat, 1 Nov 2003 13:31:27 +1100
Herbert Xu <herbert@gondor.apana.org.au> wrote:
> In ll_merge_requests_fn, it is checking blk_hw_contig_segments even if
> blk_phys_contig_segments succeeds. This means that it may cause two
> physically contiguous segments to be separated because the hw check
> fails.
Your analysis assumes that phys contig implies hw contig, I
believe it does not. There may be limitations in the VMERGE
mechanism a platform implements that causes this situation to
arise.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [BLOCK] phys_contig implies hw_contig
2003-11-02 4:45 ` David S. Miller
@ 2003-11-02 4:47 ` Herbert Xu
2003-11-02 22:10 ` Herbert Xu
0 siblings, 1 reply; 5+ messages in thread
From: Herbert Xu @ 2003-11-02 4:47 UTC (permalink / raw)
To: David S. Miller; +Cc: axboe, linux-kernel
On Sat, Nov 01, 2003 at 08:45:47PM -0800, David S. Miller wrote:
> On Sat, 1 Nov 2003 13:31:27 +1100
> Herbert Xu <herbert@gondor.apana.org.au> wrote:
>
> > In ll_merge_requests_fn, it is checking blk_hw_contig_segments even if
> > blk_phys_contig_segments succeeds. This means that it may cause two
> > physically contiguous segments to be separated because the hw check
> > fails.
>
> Your analysis assumes that phys contig implies hw contig, I
> believe it does not. There may be limitations in the VMERGE
> mechanism a platform implements that causes this situation to
> arise.
OK, if that's the case, then we better change blk_recount_segments
as it assumes this.
Cheers,
--
Debian GNU/Linux 3.0 is out! ( http://www.debian.org/ )
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [BLOCK] phys_contig implies hw_contig
2003-11-02 4:47 ` Herbert Xu
@ 2003-11-02 22:10 ` Herbert Xu
2003-11-03 22:40 ` David S. Miller
0 siblings, 1 reply; 5+ messages in thread
From: Herbert Xu @ 2003-11-02 22:10 UTC (permalink / raw)
To: David S. Miller; +Cc: axboe, linux-kernel
On Sun, Nov 02, 2003 at 03:47:34PM +1100, herbert wrote:
> On Sat, Nov 01, 2003 at 08:45:47PM -0800, David S. Miller wrote:
>
> > Your analysis assumes that phys contig implies hw contig, I
> > believe it does not. There may be limitations in the VMERGE
> > mechanism a platform implements that causes this situation to
> > arise.
>
> OK, if that's the case, then we better change blk_recount_segments
> as it assumes this.
Bug David that can't be right. If two segments are physically contiguous,
then they don't need to be remapped to be virtually continguous, right?
--
Debian GNU/Linux 3.0 is out! ( http://www.debian.org/ )
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [BLOCK] phys_contig implies hw_contig
2003-11-02 22:10 ` Herbert Xu
@ 2003-11-03 22:40 ` David S. Miller
0 siblings, 0 replies; 5+ messages in thread
From: David S. Miller @ 2003-11-03 22:40 UTC (permalink / raw)
To: Herbert Xu; +Cc: axboe, linux-kernel
On Mon, 3 Nov 2003 09:10:26 +1100
Herbert Xu <herbert@gondor.apana.org.au> wrote:
> On Sun, Nov 02, 2003 at 03:47:34PM +1100, herbert wrote:
> > On Sat, Nov 01, 2003 at 08:45:47PM -0800, David S. Miller wrote:
> >
> > > Your analysis assumes that phys contig implies hw contig, I
> > > believe it does not. There may be limitations in the VMERGE
> > > mechanism a platform implements that causes this situation to
> > > arise.
> >
> > OK, if that's the case, then we better change blk_recount_segments
> > as it assumes this.
>
> Bug David that can't be right. If two segments are physically contiguous,
> then they don't need to be remapped to be virtually continguous, right?
Yes it sounds silly.
To be honest I'm more concerned that things are consistent.
Therefore I recommend that your original patch is applied.
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2003-11-03 22:46 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2003-11-01 2:31 [BLOCK] phys_contig implies hw_contig Herbert Xu
2003-11-02 4:45 ` David S. Miller
2003-11-02 4:47 ` Herbert Xu
2003-11-02 22:10 ` Herbert Xu
2003-11-03 22:40 ` David S. Miller
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