On Wed 13-04-11 16:59:39, Wu Fengguang wrote: > When dd in 512bytes, balance_dirty_pages_ratelimited() could be called 8 > times for the same page, but obviously the page is only dirtied once. > > Fix it with a (slightly racy) PageDirty() test. > > Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> > --- > mm/filemap.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > --- linux-next.orig/mm/filemap.c 2011-04-13 16:46:01.000000000 +0800 > +++ linux-next/mm/filemap.c 2011-04-13 16:47:26.000000000 +0800 > @@ -2313,6 +2313,7 @@ static ssize_t generic_perform_write(str > long status = 0; > ssize_t written = 0; > unsigned int flags = 0; > + unsigned int dirty; > > /* > * Copies from kernel address space cannot fail (NFSD is a big user). > @@ -2361,6 +2362,7 @@ again: > pagefault_enable(); > flush_dcache_page(page); > > + dirty = PageDirty(page); This isn't completely right as we sometimes dirty the page in ->write_begin() (see e.g. block_write_begin() when we allocate blocks under an already uptodate page) and in such cases we would not call balance_dirty_pages(). So I'm not sure we can really do this optimization (although it's sad)... > mark_page_accessed(page); > status = a_ops->write_end(file, mapping, pos, bytes, copied, > page, fsdata); > @@ -2387,7 +2389,8 @@ again: > pos += copied; > written += copied; > > - balance_dirty_pages_ratelimited(mapping); > + if (!dirty) > + balance_dirty_pages_ratelimited(mapping); > > } while (iov_iter_count(i)); Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx 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>