linux-kernel - RE: [patch] optimize o_direct on block device

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Date:	Thu, 11 Jan 2007 13:51:04 -0800
From:	"Chen, Kenneth W" <kenneth.w.chen@...el.com>
To:	"'Randy Dunlap'" <randy.dunlap@...cle.com>
Cc:	"'Andrew Morton'" <akpm@...l.org>, "Michael Reed" <mdr@....com>,
	"'Zach Brown'" <zach.brown@...cle.com>,
	"'Chris Mason'" <chris.mason@...cle.com>,
	"Christoph Hellwig" <hch@...radead.org>,
	"linux-kernel" <linux-kernel@...r.kernel.org>,
	"Jeremy Higdon" <jeremy@....com>, "David Chinner" <dgc@....com>
Subject: RE: [patch] optimize o_direct on block device - v3

Randy Dunlap wrote on Thursday, January 11, 2007 1:45 PM
> > +/* return a pge back to pvec array */
> 
> is pge just a typo or some other tla that i don't know?
> (not portland general electric or pacific gas & electric)


Typo with fat fingers. Thanks for catching it. Full patch with typo fixed.



[patch] fix blk_direct_IO bio preparation.

For large size DIO that needs multiple bio, one full page worth of data
was lost at the boundary of bio's maximum sector or segment limits.
After a bio is full and got submitted.  The outer while (nbytes) { ... }
loop will allocate a new bio and just march on to index into next page.
It just forget about the page that bio_add_page() rejected when previous
bio is full.  Fix it by put the rejected page back to pvec so we pick it
up again for the next bio.


Signed-off-by: Ken Chen <kenneth.w.chen@...el.com>

diff -Nurp linux-2.6.20-rc4/fs/block_dev.c linux-2.6.20.ken/fs/block_dev.c
--- linux-2.6.20-rc4/fs/block_dev.c	2007-01-06 21:45:51.000000000 -0800
+++ linux-2.6.20.ken/fs/block_dev.c	2007-01-10 19:54:53.000000000 -0800
@@ -190,6 +190,12 @@ static struct page *blk_get_page(unsigne
 	return pvec->page[pvec->idx++];
 }
 
+/* return a page back to pvec array */
+static void blk_unget_page(struct page *page, struct pvec *pvec)
+{
+	pvec->page[--pvec->idx] = page;
+}
+
 static ssize_t
 blkdev_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
 		 loff_t pos, unsigned long nr_segs)
@@ -278,6 +284,8 @@ same_bio:
 				count = min(count, nbytes);
 				goto same_bio;
 			}
+		} else {
+			blk_unget_page(page, &pvec);
 		}
 
 		/* bio is ready, submit it */
-
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