On Wed, 1 Feb 2012 15:10:17 -0500 Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: > On Wed, Feb 01, 2012 at 04:18:07AM -0500, Christoph Hellwig wrote: > > On Tue, Jan 31, 2012 at 10:36:53PM -0500, Vivek Goyal wrote: > > > I still see that IO is being submitted one page at a time. The only > > > real difference seems to be that queue unplug happening at random times > > > and many a times we are submitting much smaller requests (40 sectors, 48 > > > sectors etc). > > > > This is expected given that the block device node uses > > block_read_full_page, and not mpage_readpage(s). > > What is the difference between block_read_full_page() and > mpage_readpage(). block_read_full_page() will attach buffer_heads to the page and will perform IO via those buffer_heads. mpage_readpage() feeds the page directly to the BIO layer and leaves it without attached buffer_heads. > IOW, why block device does not use mpage_readpage(s) > interface? We've tried it in the past and problems ensued. A quick google search for blkdev_readpages turns up stuff like http://us.generation-nt.com/answer/patch-add-readpages-support-block-devices-help-201462802.html > Applying following patch improved the speed from 110MB/s to more than > 230MB/s. Yeah. It should be doable - it would be a matter of hunting down and squishing the oddball corner cases. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>