Messages in this thread Patch in this message | | | Date | Tue, 25 Nov 2008 21:44:34 +0000 (GMT) | From | Hugh Dickins <> | Subject | [PATCH 6/9] swapfile: swapon use discard (trim) |
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When adding swap, all the old data on swap can be forgotten: sys_swapon() discard all but the header page of the swap partition (or every extent but the header of the swap file), to give a solidstate swap device the opportunity to optimize its wear-levelling.
If that succeeds, note SWP_DISCARDABLE for later use, and report it with a "D" at the right end of the kernel's "Adding ... swap" message. Perhaps something should be shown in /proc/swaps (swapon -s), but we have to be more cautious before making any addition to that format.
Signed-off-by: Hugh Dickins <hugh@veritas.com> --- swapfile.c cleanup patches 0-5 just went to linux-mm: patches 6-9 may be of wider interest, so I'm extending the Cc list for them.
include/linux/swap.h | 1 + mm/swapfile.c | 39 +++++++++++++++++++++++++++++++++++++-- 2 files changed, 38 insertions(+), 2 deletions(-)
--- swapfile5/include/linux/swap.h 2008-11-25 12:41:31.000000000 +0000 +++ swapfile6/include/linux/swap.h 2008-11-25 12:41:34.000000000 +0000 @@ -120,6 +120,7 @@ struct swap_extent { enum { SWP_USED = (1 << 0), /* is slot in swap_info[] used? */ SWP_WRITEOK = (1 << 1), /* ok to write to this swap? */ + SWP_DISCARDABLE = (1 << 2), /* blkdev supports discard */ /* add others here before... */ SWP_SCANNING = (1 << 8), /* refcount in scan_swap_map */ }; --- swapfile5/mm/swapfile.c 2008-11-25 12:41:31.000000000 +0000 +++ swapfile6/mm/swapfile.c 2008-11-25 12:41:34.000000000 +0000 @@ -84,6 +84,37 @@ void swap_unplug_io_fn(struct backing_de up_read(&swap_unplug_sem); } +/* + * swapon tell device that all the old swap contents can be discarded, + * to allow the swap device to optimize its wear-levelling. + */ +static int discard_swap(struct swap_info_struct *si) +{ + struct swap_extent *se; + int err = 0; + + list_for_each_entry(se, &si->extent_list, list) { + sector_t start_block = se->start_block << (PAGE_SHIFT - 9); + pgoff_t nr_blocks = se->nr_pages << (PAGE_SHIFT - 9); + + if (se->start_page == 0) { + /* Do not discard the swap header page! */ + start_block += 1 << (PAGE_SHIFT - 9); + nr_blocks -= 1 << (PAGE_SHIFT - 9); + if (!nr_blocks) + continue; + } + + err = blkdev_issue_discard(si->bdev, start_block, + nr_blocks, GFP_KERNEL); + if (err) + break; + + cond_resched(); + } + return err; /* That will often be -EOPNOTSUPP */ +} + #define SWAPFILE_CLUSTER 256 #define LATENCY_LIMIT 256 @@ -1649,6 +1680,9 @@ asmlinkage long sys_swapon(const char __ goto bad_swap; } + if (discard_swap(p) == 0) + p->flags |= SWP_DISCARDABLE; + mutex_lock(&swapon_mutex); spin_lock(&swap_lock); if (swap_flags & SWAP_FLAG_PREFER) @@ -1662,9 +1696,10 @@ asmlinkage long sys_swapon(const char __ total_swap_pages += nr_good_pages; printk(KERN_INFO "Adding %uk swap on %s. " - "Priority:%d extents:%d across:%lluk\n", + "Priority:%d extents:%d across:%lluk%s\n", nr_good_pages<<(PAGE_SHIFT-10), name, p->prio, - nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10)); + nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10), + (p->flags & SWP_DISCARDABLE) ? " D" : ""); /* insert swap space into swap_list: */ prev = -1;
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