* Does swap_set_page_dirty() calling ->set_page_dirty() make sense? @ 2012-09-17 16:35 Jan Kara 2012-09-17 19:15 ` Hugh Dickins 0 siblings, 1 reply; 6+ messages in thread From: Jan Kara @ 2012-09-17 16:35 UTC (permalink / raw) To: linux-mm [-- Attachment #1: Type: text/plain, Size: 781 bytes --] Hi, I tripped over a crash in reiserfs which happened due to PageSwapCache page being passed to reiserfs_set_page_dirty(). Now it's not that hard to make reiserfs_set_page_dirty() check that case but I really wonder: Does it make sense to call mapping->a_ops->set_page_dirty() for a PageSwapCache page? The page is going to be written via direct IO so from the POV of the filesystem there's no need for any dirtiness tracking. Also there are several ->set_page_dirty() implementations which will spectacularly crash because they do things like page->mapping->host, or call __set_page_dirty_buffers() which expects buffer heads in page->private. Or what is the reason for calling filesystem's set_page_dirty() function? Honza -- Jan Kara <jack@suse.cz> SUSE Labs, CR [-- Attachment #2: 0001-mm-Remove-swap_set_page_dirty.patch --] [-- Type: text/x-patch, Size: 0 bytes --] ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Does swap_set_page_dirty() calling ->set_page_dirty() make sense? 2012-09-17 16:35 Does swap_set_page_dirty() calling ->set_page_dirty() make sense? Jan Kara @ 2012-09-17 19:15 ` Hugh Dickins 2012-09-18 2:16 ` Jan Kara 2012-09-18 9:58 ` Mel Gorman 0 siblings, 2 replies; 6+ messages in thread From: Hugh Dickins @ 2012-09-17 19:15 UTC (permalink / raw) To: Jan Kara; +Cc: Mel Gorman, linux-mm On Mon, 17 Sep 2012, Jan Kara wrote: > > I tripped over a crash in reiserfs which happened due to PageSwapCache > page being passed to reiserfs_set_page_dirty(). Now it's not that hard to > make reiserfs_set_page_dirty() check that case but I really wonder: Does it > make sense to call mapping->a_ops->set_page_dirty() for a PageSwapCache > page? The page is going to be written via direct IO so from the POV of the > filesystem there's no need for any dirtiness tracking. Also there are > several ->set_page_dirty() implementations which will spectacularly crash > because they do things like page->mapping->host, or call > __set_page_dirty_buffers() which expects buffer heads in page->private. > Or what is the reason for calling filesystem's set_page_dirty() function? This is a question for Mel, really: it used not to call the filesystem. But my reading of the 3.6 code says that it still will not call the filesystem, unless the filesystem (only nfs) provides a swap_activate method, which should be the only case in which SWP_FILE gets set. And I rather think Mel does want to use the filesystem set_page_dirty in that case. Am I misreading? Did you see this on a vanilla kernel? Or is it possible that you have a private patch merged in, with something else sharing the SWP_FILE bit (defined in include/linux/swap.h) by mistake? Hugh > [PATCH] mm: Remove swap_set_page_dirty() > > It doesn't make much sense to call filesystem's ->set_page_dirty() method for > PageSwapCache page. It will be written through direct IO so filesystem doesn't > care about its dirtiness and several filesystems actually don't count with such > pages getting into their ->set_page_dirty() functions. > > Signed-off-by: Jan Kara <jack@suse.cz> > --- > mm/page_io.c | 12 ------------ > mm/swap_state.c | 2 +- > 2 files changed, 1 insertions(+), 13 deletions(-) > > diff --git a/mm/page_io.c b/mm/page_io.c > index 78eee32..8520a4f 100644 > --- a/mm/page_io.c > +++ b/mm/page_io.c > @@ -278,15 +278,3 @@ int swap_readpage(struct page *page) > out: > return ret; > } > - > -int swap_set_page_dirty(struct page *page) > -{ > - struct swap_info_struct *sis = page_swap_info(page); > - > - if (sis->flags & SWP_FILE) { > - struct address_space *mapping = sis->swap_file->f_mapping; > - return mapping->a_ops->set_page_dirty(page); > - } else { > - return __set_page_dirty_no_writeback(page); > - } > -} > diff --git a/mm/swap_state.c b/mm/swap_state.c > index 0cb36fb..01852cd 100644 > --- a/mm/swap_state.c > +++ b/mm/swap_state.c > @@ -27,7 +27,7 @@ > */ > static const struct address_space_operations swap_aops = { > .writepage = swap_writepage, > - .set_page_dirty = swap_set_page_dirty, > + .set_page_dirty = set_page_dirty_no_writeback, > .migratepage = migrate_page, > }; > > -- > 1.7.1 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Does swap_set_page_dirty() calling ->set_page_dirty() make sense? 2012-09-17 19:15 ` Hugh Dickins @ 2012-09-18 2:16 ` Jan Kara 2012-09-18 8:51 ` Petr Tesarik 2012-09-18 9:58 ` Mel Gorman 1 sibling, 1 reply; 6+ messages in thread From: Jan Kara @ 2012-09-18 2:16 UTC (permalink / raw) To: Hugh Dickins; +Cc: Jan Kara, Mel Gorman, linux-mm On Mon 17-09-12 12:15:46, Hugh Dickins wrote: > On Mon, 17 Sep 2012, Jan Kara wrote: > > > > I tripped over a crash in reiserfs which happened due to PageSwapCache > > page being passed to reiserfs_set_page_dirty(). Now it's not that hard to > > make reiserfs_set_page_dirty() check that case but I really wonder: Does it > > make sense to call mapping->a_ops->set_page_dirty() for a PageSwapCache > > page? The page is going to be written via direct IO so from the POV of the > > filesystem there's no need for any dirtiness tracking. Also there are > > several ->set_page_dirty() implementations which will spectacularly crash > > because they do things like page->mapping->host, or call > > __set_page_dirty_buffers() which expects buffer heads in page->private. > > Or what is the reason for calling filesystem's set_page_dirty() function? > > This is a question for Mel, really: it used not to call the filesystem. > > But my reading of the 3.6 code says that it still will not call the > filesystem, unless the filesystem (only nfs) provides a swap_activate > method, which should be the only case in which SWP_FILE gets set. > And I rather think Mel does want to use the filesystem set_page_dirty > in that case. Am I misreading? > > Did you see this on a vanilla kernel? Or is it possible that you have > a private patch merged in, with something else sharing the SWP_FILE bit > (defined in include/linux/swap.h) by mistake? Argh, sorry. It is indeed a SLES specific bug. I missed that SWP_FILE bit gets set only when swap_activate() is provided (SLES code works a bit differently in this area but I wasn't really looking into that since I was focused elsewhere). So just one minor nit for Mel. SWP_FILE looks like a bit confusing name for a flag that gets set only for some swap files ;) At least I didn't pay attention to it because I thought it's set for all of them. Maybe call it SWP_FILE_CALL_AOPS or something like that? Thanks Hugh for having a look. Honza -- Jan Kara <jack@suse.cz> SUSE Labs, CR -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Does swap_set_page_dirty() calling ->set_page_dirty() make sense? 2012-09-18 2:16 ` Jan Kara @ 2012-09-18 8:51 ` Petr Tesarik 2012-09-18 10:02 ` Mel Gorman 0 siblings, 1 reply; 6+ messages in thread From: Petr Tesarik @ 2012-09-18 8:51 UTC (permalink / raw) To: Jan Kara; +Cc: Hugh Dickins, Mel Gorman, linux-mm Dne Út 18. září 2012 04:16:27 Jan Kara napsal(a): > On Mon 17-09-12 12:15:46, Hugh Dickins wrote: > > On Mon, 17 Sep 2012, Jan Kara wrote: > > > I tripped over a crash in reiserfs which happened due to > > > PageSwapCache > > > > > > page being passed to reiserfs_set_page_dirty(). Now it's not that hard > > > to make reiserfs_set_page_dirty() check that case but I really wonder: > > > Does it make sense to call mapping->a_ops->set_page_dirty() for a > > > PageSwapCache page? The page is going to be written via direct IO so > > > from the POV of the filesystem there's no need for any dirtiness > > > tracking. Also there are several ->set_page_dirty() implementations > > > which will spectacularly crash because they do things like > > > page->mapping->host, or call > > > __set_page_dirty_buffers() which expects buffer heads in page->private. > > > Or what is the reason for calling filesystem's set_page_dirty() > > > function? > > > > This is a question for Mel, really: it used not to call the filesystem. > > > > But my reading of the 3.6 code says that it still will not call the > > filesystem, unless the filesystem (only nfs) provides a swap_activate > > method, which should be the only case in which SWP_FILE gets set. > > And I rather think Mel does want to use the filesystem set_page_dirty > > in that case. Am I misreading? > > > > Did you see this on a vanilla kernel? Or is it possible that you have > > a private patch merged in, with something else sharing the SWP_FILE bit > > (defined in include/linux/swap.h) by mistake? > > Argh, sorry. It is indeed a SLES specific bug. I missed that SWP_FILE bit > gets set only when swap_activate() is provided (SLES code works a bit > differently in this area but I wasn't really looking into that since I was > focused elsewhere). > > So just one minor nit for Mel. SWP_FILE looks like a bit confusing name for > a flag that gets set only for some swap files ;) At least I didn't pay > attention to it because I thought it's set for all of them. Maybe call it > SWP_FILE_CALL_AOPS or something like that? Same here. In fact, I believed that other filesystems only work by accident (because they don't have to access the mapping). I'm not even sure about the semantics of the swap_activate operation. Is this documented somewhere? Petr Tesarik SUSE Linux -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Does swap_set_page_dirty() calling ->set_page_dirty() make sense? 2012-09-18 8:51 ` Petr Tesarik @ 2012-09-18 10:02 ` Mel Gorman 0 siblings, 0 replies; 6+ messages in thread From: Mel Gorman @ 2012-09-18 10:02 UTC (permalink / raw) To: Petr Tesarik; +Cc: Jan Kara, Hugh Dickins, linux-mm On Tue, Sep 18, 2012 at 10:51:50AM +0200, Petr Tesarik wrote: > > <SNIP> > > > > So just one minor nit for Mel. SWP_FILE looks like a bit confusing name for > > a flag that gets set only for some swap files ;) At least I didn't pay > > attention to it because I thought it's set for all of them. Maybe call it > > SWP_FILE_CALL_AOPS or something like that? > I guess it would be a slightly better name all right. > Same here. In fact, I believed that other filesystems only work by accident > (because they don't have to access the mapping). I'm not even sure about the > semantics of the swap_activate operation. Is this documented somewhere? > Documentation/filesystems/vfs.txt *briefly* describes what swap_activate() does even though now that I read it I see that it's inaccurate. It says that it proxies to the address spaces swapin_[out|in] method but it really gets proxied to the direct_IO interface for writes and readpage for reads (direct_IO could have been used for reads but my recollection was that the locking was very awkward). -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Does swap_set_page_dirty() calling ->set_page_dirty() make sense? 2012-09-17 19:15 ` Hugh Dickins 2012-09-18 2:16 ` Jan Kara @ 2012-09-18 9:58 ` Mel Gorman 1 sibling, 0 replies; 6+ messages in thread From: Mel Gorman @ 2012-09-18 9:58 UTC (permalink / raw) To: Hugh Dickins; +Cc: Jan Kara, linux-mm On Mon, Sep 17, 2012 at 12:15:46PM -0700, Hugh Dickins wrote: > On Mon, 17 Sep 2012, Jan Kara wrote: > > > > I tripped over a crash in reiserfs which happened due to PageSwapCache > > page being passed to reiserfs_set_page_dirty(). Now it's not that hard to > > make reiserfs_set_page_dirty() check that case but I really wonder: Does it > > make sense to call mapping->a_ops->set_page_dirty() for a PageSwapCache > > page? The page is going to be written via direct IO so from the POV of the > > filesystem there's no need for any dirtiness tracking. Also there are > > several ->set_page_dirty() implementations which will spectacularly crash > > because they do things like page->mapping->host, or call > > __set_page_dirty_buffers() which expects buffer heads in page->private. > > Or what is the reason for calling filesystem's set_page_dirty() function? > > This is a question for Mel, really: it used not to call the filesystem. > And now it should only be called if SWP_FILE is set to perform read/write of pages through the filesystem. In practice I only expect this to happen when a swapfile is activated on NFS. > But my reading of the 3.6 code says that it still will not call the > filesystem, unless the filesystem (only nfs) provides a swap_activate > method, which should be the only case in which SWP_FILE gets set. > And I rather think Mel does want to use the filesystem set_page_dirty > in that case. Am I misreading? > That was the intention at least. > Did you see this on a vanilla kernel? Or is it possible that you have > a private patch merged in, with something else sharing the SWP_FILE bit > (defined in include/linux/swap.h) by mistake? > I see that Jan followed up that this was observed on SLES. The implementaiton there is based on a much earlier revision of swap-over-NFS than what was finally merged to mainline. I'll check it out. Thanks. -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2012-09-18 10:02 UTC | newest] Thread overview: 6+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2012-09-17 16:35 Does swap_set_page_dirty() calling ->set_page_dirty() make sense? Jan Kara 2012-09-17 19:15 ` Hugh Dickins 2012-09-18 2:16 ` Jan Kara 2012-09-18 8:51 ` Petr Tesarik 2012-09-18 10:02 ` Mel Gorman 2012-09-18 9:58 ` Mel Gorman
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