Messages in this thread Patch in this message | | | Date | Mon, 1 Dec 2008 11:19:22 +0800 | From | Wu Fengguang <> | Subject | [PATCH] nfs: remove redundant tests on reading new pages |
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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@netapp.com> Signed-off-by: Wu Fengguang <wfg@linux.intel.com> --- 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.
--- 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);
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