On Sun, 12 Apr 2009 15:16:05 +0800 Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote: > [This patch may not necessarily be merged, but at least we should > be aware of the problem.] > > When user space requests past-EOF data, do_generic_file_read() will > issue a bonus readpage call, which may be unfavorable. > > do_generic_file_read: > -> find_page: > -> find_get_page() = NULL > -> page_cache_sync_readahead() > -> find_get_page() = NULL > -> no_cached_page: > -> readpage: > -> nfs_readpage() = error > -> readpage_error: > > Reported-by: Xu Chenfeng <xcf@xxxxxxxxxxx> > Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> > --- > mm/filemap.c | 5 +++++ > 1 file changed, 5 insertions(+) > > --- mm.orig/mm/filemap.c > +++ mm/mm/filemap.c > @@ -1269,6 +1269,11 @@ readpage_error: > goto out; > > no_cached_page: > + isize = i_size_read(inode); > + end_index = (isize - 1) >> PAGE_CACHE_SHIFT; > + if (unlikely(!isize || index > end_index)) > + goto out; > + > /* > * Ok, it wasn't cached, so we need to create a new > * page.. Is this a problem which needs to be solved? userspace does something silly and the kernel behaves a bit suboptimally? If thats the only problem here then it's not worth adding fastpath cycles to fix it? -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
