> From: Minchan Kim [mailto:minchan@xxxxxxxxxx] > Subject: Re: [RFC] mm: remove swapcache page early > > Hi Dan, > > On Wed, Mar 27, 2013 at 03:24:00PM -0700, Dan Magenheimer wrote: > > > From: Hugh Dickins [mailto:hughd@xxxxxxxxxx] > > > Subject: Re: [RFC] mm: remove swapcache page early > > > > > > I believe the answer is for frontswap/zmem to invalidate the frontswap > > > copy of the page (to free up the compressed memory when possible) and > > > SetPageDirty on the PageUptodate PageSwapCache page when swapping in > > > (setting page dirty so nothing will later go to read it from the > > > unfreed location on backing swap disk, which was never written). > > > > There are two duplication issues: (1) When can the page be removed > > from the swap cache after a call to frontswap_store; and (2) When > > can the page be removed from the frontswap storage after it > > has been brought back into memory via frontswap_load. > > > > This patch from Minchan addresses (1). The issue you are raising > > No. I am addressing (2). > > > here is (2). You may not know that (2) has recently been solved > > in frontswap, at least for zcache. See frontswap_exclusive_gets_enabled. > > If this is enabled (and it is for zcache but not yet for zswap), > > what you suggest (SetPageDirty) is what happens. > > I am blind on zcache so I didn't see it. Anyway, I'd like to address it > on zram and zswap. Zswap can enable it trivially by adding a function call in init_zswap. (Note that it is not enabled by default for all frontswap backends because it is another complicated tradeoff of cpu time vs memory space that needs more study on a broad set of workloads.) I wonder if something like this would have a similar result for zram? (Completely untested... snippet stolen from swap_entry_free with SetPageDirty added... doesn't compile yet, but should give you the idea.) diff --git a/mm/page_io.c b/mm/page_io.c index 56276fe..2d10988 100644 --- a/mm/page_io.c +++ b/mm/page_io.c @@ -81,7 +81,17 @@ void end_swap_bio_read(struct bio *bio, int err) iminor(bio->bi_bdev->bd_inode), (unsigned long long)bio->bi_sector); } else { + struct swap_info_struct *sis; + SetPageUptodate(page); + sis = page_swap_info(page); + if (sis->flags & SWP_BLKDEV) { + struct gendisk *disk = sis->bdev->bd_disk; + if (disk->fops->swap_slot_free_notify) { + SetPageDirty(page); + disk->fops->swap_slot_free_notify(sis->bdev, + offset); + } + } } unlock_page(page); bio_put(bio); -- 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