On Mon, Dec 01, 2008 at 11:19:22AM +0800, Wu Fengguang wrote: > aops->readpages() and its NFS helper readpage_async_filler() will only > be called to do readahead I/O for newly allocated pages. So it's not > necessary to test for the always 0 dirty/uptodate page flags. > > The removal of nfs_wb_page() call also fixes a readahead bug: the NFS > readahead has been synchronous since 2.6.23, because that call will > clear PG_readahead, which is the reminder for asynchronous readahead. > > More background: the PG_readahead page flag is shared with PG_reclaim, > one for read path and the other for write path. clear_page_dirty_for_io() > unconditionally clears PG_readahead to prevent possible readahead residuals, > assuming itself to be always called in the write path. However, NFS is one > and the only exception in that it _always_ calls clear_page_dirty_for_io() > in the read path, i.e. for readpages()/readpage(). > > Cc: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx> > Signed-off-by: Wu Fengguang <wfg@xxxxxxxxxxxxxxx> > --- > fs/nfs/read.c | 6 ------ > 1 file changed, 6 deletions(-) > > This bug was found when playing with my readahead tracing module posted at > http://lkml.org/lkml/2008/11/27/373 and confirmed to work. > > The NFS readahead traces are now > > [ 59.972526] readahead-initial0(pid=3646(dd), dev=00:0f(0:f), ino=293189(1G), req=0+25, ra=0+60-30, async=0) = 60 > [ 59.992734] readahead-subsequent(pid=3646(dd), dev=00:0f(0:f), ino=293189(1G), req=30+20, ra=60+30-30, async=1) = 30 > [ 60.030900] readahead-subsequent(pid=3646(dd), dev=00:0f(0:f), ino=293189(1G), req=60+15, ra=90+30-30, async=1) = 30 > [ 60.031687] readahead-subsequent(pid=3646(dd), dev=00:0f(0:f), ino=293189(1G), req=90+10, ra=120+30-30, async=1) = 30 > > The async field was always 0 before this patch. On the trace messages: they are generated by the command 'dd if=/tmp/sparse/1G of=/dev/null bs=100k count=9' with readahead_size=120k. The printk for generating the messages is: printk(KERN_DEBUG "readahead-%s(pid=%d(%s), dev=%02x:%02x(%s), " "ino=%lu(%s), req=%lu+%lu, ra=%lu+%d-%d, async=%d) = %d\n", ra_pattern_names[pattern], current->pid, current->comm, MAJOR(mapping->host->i_sb->s_dev), MINOR(mapping->host->i_sb->s_dev), mapping->host->i_sb->s_id, mapping->host->i_ino, filp->f_path.dentry->d_name.name, offset, req_size, ra->start, ra->size, ra->async_size, async, actual); Thanks, Fengguang > --- linux-2.6.orig/fs/nfs/read.c > +++ linux-2.6/fs/nfs/read.c > @@ -533,12 +533,6 @@ readpage_async_filler(void *data, struct > unsigned int len; > int error; > > - error = nfs_wb_page(inode, page); > - if (error) > - goto out_unlock; > - if (PageUptodate(page)) > - goto out_unlock; > - > len = nfs_page_length(page); > if (len == 0) > return nfs_return_empty_page(page); -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
