On Wed, Jul 18 2007, Hugh Dickins wrote: > On Wed, 18 Jul 2007, Jens Axboe wrote: > > > > We have these checks scattered, makes sense to put them in > > set_page_dirty() instead. This also fixes a bug where __bio_unmap_user() > > does set_page_dirty_lock() without checking for a compound page, instead > > of adding one more check we move it to set_page_dirty(). > > > > Signed-off-by: Jens Axboe <[EMAIL PROTECTED]> > > > > diff --git a/fs/bio.c b/fs/bio.c > > index cd888f9..ff96cd9 100644 > > --- a/fs/bio.c > > +++ b/fs/bio.c > > @@ -902,7 +902,7 @@ void bio_set_pages_dirty(struct bio *bio) > > for (i = 0; i < bio->bi_vcnt; i++) { > > struct page *page = bvec[i].bv_page; > > > > - if (page && !PageCompound(page)) > > + if (page) > > set_page_dirty_lock(page); > > } > > } > > diff --git a/fs/direct-io.c b/fs/direct-io.c > > index 52bb263..72195bc 100644 > > --- a/fs/direct-io.c > > +++ b/fs/direct-io.c > > @@ -426,7 +426,7 @@ static int dio_bio_complete(struct dio *dio, struct bio > > *bio) > > for (page_no = 0; page_no < bio->bi_vcnt; page_no++) { > > struct page *page = bvec[page_no].bv_page; > > > > - if (dio->rw == READ && !PageCompound(page)) > > + if (dio->rw == READ) > > set_page_dirty_lock(page); > > page_cache_release(page); > > } > > diff --git a/mm/page-writeback.c b/mm/page-writeback.c > > index 886ea0d..3c590b9 100644 > > --- a/mm/page-writeback.c > > +++ b/mm/page-writeback.c > > @@ -861,8 +861,12 @@ EXPORT_SYMBOL(redirty_page_for_writepage); > > */ > > int fastcall set_page_dirty(struct page *page) > > { > > - struct address_space *mapping = page_mapping(page); > > + struct address_space *mapping; > > + > > + if (unlikely(PageCompound(page))) > > + return 0; > > > > + mapping = page_mapping(page); > > if (likely(mapping)) { > > int (*spd)(struct page *) = mapping->a_ops->set_page_dirty; > > #ifdef CONFIG_BLOCK > > I'd prefer it if we just remove those two tests from fs without > adding one into set_page_dirty at all; though I've not tested > that recently (replying before remembering the easiest way to > do so), and others may disagree. > > The real reason for those tests was that pre-2.6.16 a compound page > stored its destructor in page[1].mapping: which went badly wrong if > that constituent page ever ended up being passed to set_page_dirty. > > I moved it somewhere safer in 41d78ba55037468e6c86c53e3076d1a74841de39 > but didn't have the courage to remove those tests you're now removing: > the earlier we skip out from that case, the more efficiently it's > handled, I didn't want to slow those paths down in case they were > important to someone. > > So I'd be glad to see those tests now gone without replacement.
OK, you clearly have more knowledge in that area than I, but I do wish that you would have made a note in the code at least to remove things like this. It's pretty ugly to have superflous tests like that, especially since there was not even a comment saying _why_ you could not call set_page_dirty() on a compound page. I see it in the commit text, but nobody looking at fs/bio.c or fs/direct-io.c would directly find any reference of that. Could you submit a patch removing the tests? -- Jens Axboe - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/