On Thu, Mar 28, 2013 at 11:19:12AM -0700, Dan Magenheimer wrote: > > 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.) Nice idea! After I see your patch, I realized it was Hugh's suggestion and you implemented it in proper place. Will resend it after testing. Maybe nextweek. Thanks! > > 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=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> -- Kind regards, Minchan Kim -- 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>