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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>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Matthew Wilcox <matthew@wil.cx>
Cc: Joern Engel <joern@logfs.org>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Donjun Shin <djshin90@gmail.com>
Cc: Tejun Heo <teheo@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2009-01-06 14:39:51 -08:00 committed by Linus Torvalds
parent ebebbbe904
commit 6a6ba83175
2 changed files with 38 additions and 2 deletions
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1
include/linux/swap.h
View File

@ -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 */
};

39
mm/swapfile.c
View File

@ -84,6 +84,37 @@ void swap_unplug_io_fn(struct backing_dev_info *unused_bdi, struct page *page)
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
@ -1658,6 +1689,9 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
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)
@ -1671,9 +1705,10 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
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;