From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx137.postini.com [74.125.245.137]) by kanga.kvack.org (Postfix) with SMTP id 6F3896B0070 for ; Wed, 8 May 2013 19:42:00 -0400 (EDT) From: Minchan Kim Subject: [PATCH v3] mm: remove compressed copy from zram in-memory Date: Thu, 9 May 2013 08:41:57 +0900 Message-Id: <1368056517-31065-1-git-send-email-minchan@kernel.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Minchan Kim , Hugh Dickins , Seth Jennings , Nitin Gupta , Konrad Rzeszutek Wilk , Shaohua Li , Dan Magenheimer 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 * changelog from v3 * Rebased on next-20130508 * changelog from v1 * Add more comment Cc: Hugh Dickins Cc: Seth Jennings Cc: Nitin Gupta Cc: Konrad Rzeszutek Wilk Cc: Shaohua Li Signed-off-by: Dan Magenheimer Signed-off-by: Minchan Kim --- mm/page_io.c | 35 +++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) diff --git a/mm/page_io.c b/mm/page_io.c index a294076..527db57 100644 --- a/mm/page_io.c +++ b/mm/page_io.c @@ -21,6 +21,7 @@ #include #include #include +#include #include static struct bio *get_swap_bio(gfp_t gfp_flags, @@ -82,8 +83,42 @@ void end_swap_bio_read(struct bio *bio, int err, struct batch_complete *batch) 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) { + /* + * Swap subsystem does lazy swap slot free with + * expecting the page would be swapped out again + * so we can avoid unnecessary write if the page + * isn't redirty. + * It's good for real swap storage because we can + * reduce unnecessary I/O and enhance wear-leveling + * if you use SSD as swap device. + * But if you use in-memory swap device(ex, zram), + * it causes 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 swap out somewhere again if + * we want to reclaim it, again. + */ + 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); + } + } } + unlock_page(page); bio_put(bio); } -- 1.8.2.1 -- 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: email@kvack.org