Intruduce a new flag to make page-cluster fine-grained discards while swapping
conditional, as they can be considered detrimental to some setups. However,
keep allowing batched discards at sys_swapon() time, when enabled by the
system administrator.
Signed-off-by: Rafael Aquini <aqu...@redhat.com>
---
include/linux/swap.h | 8 +++++---
mm/swapfile.c | 12 ++++++++----
2 files changed, 13 insertions(+), 7 deletions(-)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 1701ce4..ab2e742 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -19,10 +19,11 @@ struct bio;
#define SWAP_FLAG_PREFER 0x8000 /* set if swap priority specified */
#define SWAP_FLAG_PRIO_MASK 0x7fff
#define SWAP_FLAG_PRIO_SHIFT 0
-#define SWAP_FLAG_DISCARD 0x10000 /* discard swap cluster after use */
+#define SWAP_FLAG_DISCARD 0x10000 /* enable discard for swap areas */
+#define SWAP_FLAG_DISCARD_CLUSTER 0x20000 /* discard swap clusters after use */
#define SWAP_FLAGS_VALID (SWAP_FLAG_PRIO_MASK | SWAP_FLAG_PREFER | \
- SWAP_FLAG_DISCARD)
+ SWAP_FLAG_DISCARD | SWAP_FLAG_DISCARD_CLUSTER)
static inline int current_is_kswapd(void)
{
@@ -152,8 +153,9 @@ enum {
SWP_CONTINUED = (1 << 5), /* swap_map has count continuation */
SWP_BLKDEV = (1 << 6), /* its a block device */
SWP_FILE = (1 << 7), /* set after swap_activate success */
+ SWP_CLUSTERDISCARD = (1 << 8), /* discard swap cluster after usage */
/* add others here before... */
- SWP_SCANNING = (1 << 8), /* refcount in scan_swap_map */
+ SWP_SCANNING = (1 << 9), /* refcount in scan_swap_map */
};
#define SWAP_CLUSTER_MAX 32UL
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 6c340d9..197461f 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -212,7 +212,7 @@ static unsigned long scan_swap_map(struct swap_info_struct
*si,
si->cluster_nr = SWAPFILE_CLUSTER - 1;
goto checks;
}
- if (si->flags & SWP_DISCARDABLE) {
+ if (si->flags & SWP_CLUSTERDISCARD) {
/*
* Start range check on racing allocations, in case
* they overlap the cluster we eventually decide on
@@ -322,7 +322,7 @@ checks:
if (si->lowest_alloc) {
/*
- * Only set when SWP_DISCARDABLE, and there's a scan
+ * Only set when SWP_CLUSTERDISCARD, and there's a scan
* for a free cluster in progress or just completed.
*/
if (found_free_cluster) {
@@ -2123,8 +2123,11 @@ SYSCALL_DEFINE2(swapon, const char __user *,
specialfile, int, swap_flags)
p->flags |= SWP_SOLIDSTATE;
p->cluster_next = 1 + (prandom_u32() % p->highest_bit);
}
- if ((swap_flags & SWAP_FLAG_DISCARD) && discard_swap(p) == 0)
+ if ((swap_flags & SWAP_FLAG_DISCARD) && discard_swap(p) == 0) {
p->flags |= SWP_DISCARDABLE;
+ if (swap_flags & SWAP_FLAG_DISCARD_CLUSTER)
+ p->flags |= SWP_CLUSTERDISCARD;
+ }
}
mutex_lock(&swapon_mutex);
@@ -2135,11 +2138,12 @@ SYSCALL_DEFINE2(swapon, const char __user *,
specialfile, int, swap_flags)
enable_swap_info(p, prio, swap_map, frontswap_map);
printk(KERN_INFO "Adding %uk swap on %s. "
- "Priority:%d extents:%d across:%lluk %s%s%s\n",
+ "Priority:%d extents:%d across:%lluk %s%s%s%s\n",
p->pages<<(PAGE_SHIFT-10), name->name, p->prio,
nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
(p->flags & SWP_SOLIDSTATE) ? "SS" : "",
(p->flags & SWP_DISCARDABLE) ? "D" : "",
+ (p->flags & SWP_CLUSTERDISCARD) ? "C" : "",
(frontswap_map) ? "FS" : "");
mutex_unlock(&swapon_mutex);
--
1.7.11.7
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