Hi Hugh, On Mon, Nov 21, 2016 at 07:46:28PM -0800, Hugh Dickins wrote: > On Mon, 21 Nov 2016, Minchan Kim wrote: > > From: Minchan Kim <minchan@xxxxxxxxxx> > > Date: Fri, 11 Nov 2016 15:02:57 +0900 > > Subject: [PATCH v2] mm: support anonymous stable page > > > > For developemnt for zram-swap asynchronous writeback, I found > > strange corruption of compressed page. With investigation, it > > reveals currently stable page doesn't support anonymous page. > > IOW, reuse_swap_page can reuse the page without waiting > > writeback completion so that it can corrupt data during > > zram compression. It can affect every swap device which supports > > asynchronous writeback and CRC checking as well as zRAM. > > > > Unfortunately, reuse_swap_page should be atomic so that we > > cannot wait on writeback in there so the approach in this patch > > is simply return false if we found it needs stable page. > > Although it increases memory footprint temporarily, it happens > > rarely and it should be reclaimed easily althoug it happened. > > Also, It would be better than waiting of IO completion, which > > is critial path for application latency. > > > > Cc: Hugh Dickins <hughd@xxxxxxxxxx> > > Cc: Darrick J. Wong <darrick.wong@xxxxxxxxxx> > > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> > > Acked-by: Hugh Dickins <hughd@xxxxxxxxxx> Thanks! > > Looks good, thanks: we can always optimize away that little overhead > in the PageWriteback case, if it ever shows up in someone's testing. Yeb. > > Andrew might ask if we should Cc stable (haha): I think we agree > that it's a defect we've been aware of ever since stable pages were > first proposed, but nobody has actually been troubled by it before > your async zram development: so, you're right to be fixing it ahead > of your zram changes, but we don't see a call for backporting. I thought so until I see your comment. However, I checked again and found it seems a ancient bug since zram birth. swap_writepage unlock the page right before submitting bio while it keeps the lock during rw_page operation during bdev_write_page. So, if zram_rw_page fails(e.g, -ENOMEM) and then fallback to submit_bio in __swap_writepage, the problem can occur. Hmm, I will resend patchset with zram fix part with marking the stable. Thanks, Hugh! -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>