mm: remove compressed copy from zram in-memory (b430e9d1) · Commits · 戴 / test

Swap subsystem does lazy swap slot free with expecting the page would be swapped out again so we can avoid unnecessary write. But the problem in in-memory swap(ex, zram) is that it consumes memory space until vm_swap_full(ie, used half of all of swap device) condition meet. It could be bad if we use multiple swap device, small in-memory swap and big storage swap or in-memory swap alone. This patch makes swap subsystem free swap slot as soon as swap-read is completed and make the swapcache page dirty so the page should be written out the swap device to reclaim it. It means we never lose it. I tested this patch with kernel compile workload. 1. before compile time : 9882.42 zram max wasted space by fragmentation: 13471881 byte memory space consumed by zram: 174227456 byte the number of slot free notify: 206684 2. after compile time : 9653.90 zram max wasted space by fragmentation: 11805932 byte memory space consumed by zram: 154001408 byte the number of slot free notify: 426972 [akpm@linux-foundation.org: tweak comment text] [artem.savkov@gmail.com: fix BUG due to non-swapcache pages in end_swap_bio_read()] [akpm@linux-foundation.org: invert unlikely() test, augment comment, 80-col cleanup] Signed-off-by:

Dan Magenheimer <dan.magenheimer@oracle.com> Signed-off-by:

Minchan Kim <minchan@kernel.org> Signed-off-by:

Artem Savkov <artem.savkov@gmail.com> Cc: Hugh Dickins <hughd@google.com> Cc: Seth Jennings <sjenning@linux.vnet.ibm.com> Cc: Nitin Gupta <ngupta@vflare.org> Cc: Konrad Rzeszutek Wilk <konrad@darnok.org> Cc: Shaohua Li <shli@kernel.org> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/page_io.c

+48 −2

Original line number	Original line	Diff line number	Diff line
	@@ -21,6 +21,7 @@
	#include <linux/writeback.h>		#include <linux/writeback.h>
	#include <linux/frontswap.h>		#include <linux/frontswap.h>
	#include <linux/aio.h>		#include <linux/aio.h>
			#include <linux/blkdev.h>
	#include <asm/pgtable.h>		#include <asm/pgtable.h>

	static struct bio *get_swap_bio(gfp_t gfp_flags,		static struct bio *get_swap_bio(gfp_t gfp_flags,
	@@ -80,9 +81,54 @@ void end_swap_bio_read(struct bio *bio, int err)
	imajor(bio->bi_bdev->bd_inode),		imajor(bio->bi_bdev->bd_inode),
	iminor(bio->bi_bdev->bd_inode),		iminor(bio->bi_bdev->bd_inode),
	(unsigned long long)bio->bi_sector);		(unsigned long long)bio->bi_sector);
	} else {		goto out;
			}

	SetPageUptodate(page);		SetPageUptodate(page);

			/*
			* There is no guarantee that the page is in swap cache - the software
			* suspend code (at least) uses end_swap_bio_read() against a non-
			* swapcache page. So we must check PG_swapcache before proceeding with
			* this optimization.
			*/
			if (likely(PageSwapCache(page))) {
			struct swap_info_struct *sis;

			sis = page_swap_info(page);
			if (sis->flags & SWP_BLKDEV) {
			/*
			* The swap subsystem performs lazy swap slot freeing,
			* expecting that the page will be swapped out again.
			* So we can avoid an unnecessary write if the page
			* isn't redirtied.
			* This is good for real swap storage because we can
			* reduce unnecessary I/O and enhance wear-leveling
			* if an SSD is used as the as swap device.
			* But if in-memory swap device (eg zram) is used,
			* this causes a duplicated copy between uncompressed
			* data in VM-owned memory and compressed data in
			* zram-owned memory. So let's free zram-owned memory
			* and make the VM-owned decompressed page dirty,
			* so the page should be swapped out somewhere again if
			* we again wish to reclaim it.
			*/
			struct gendisk *disk = sis->bdev->bd_disk;
			if (disk->fops->swap_slot_free_notify) {
			swp_entry_t entry;
			unsigned long offset;

			entry.val = page_private(page);
			offset = swp_offset(entry);

			SetPageDirty(page);
			disk->fops->swap_slot_free_notify(sis->bdev,
			offset);
	}		}
			}
			}

			out:
	unlock_page(page);		unlock_page(page);
	bio_put(bio);		bio_put(bio);
	}		}

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