Skip to content

Commit

Permalink
mm: swap: add a adaptive full cluster cache reclaim
Browse files Browse the repository at this point in the history 
Link all full cluster with one full list, and reclaim from it when the
allocation have ran out of all usable clusters.

There are many reason a folio can end up being in the swap cache while
having no swap count reference.  So the best way to search for such slots
is still by iterating the swap clusters.

With the list as an LRU, iterating from the oldest cluster and keep them
rotating is a very doable and clean way to free up potentially not inuse
clusters.

When any allocation failure, try reclaim and rotate only one cluster. 
This is adaptive for high order allocations they can tolerate fallback. 
So this avoids latency, and give the full cluster list an fair chance to
get reclaimed.  It release the usage stress for the fallback order 0
allocation or following up high order allocation.

If the swap device is getting very full, reclaim more aggresively to
ensure no OOM will happen.  This ensures order 0 heavy workload won't go
OOM as order 0 won't fail if any cluster still have any space.

[ryncsn@gmail.com: fix discard of full cluster]
  Link: https://lkml.kernel.org/r/CAMgjq7CWwK75_2Zi5P40K08pk9iqOcuWKL6khu=x4Yg_nXaQag@mail.gmail.com
Link: https://lkml.kernel.org/r/20240730-swap-allocator-v5-9-cb9c148b9297@kernel.org
Signed-off-by: Kairui Song <kasong@tencent.com>
Reported-by: Barry Song <21cnbao@gmail.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Kairui Song <ryncsn@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
  • Loading branch information
@ryncsn @akpm00
ryncsn authored and akpm00 committed Sep 4, 2024
1 parent 661383c commit 2cacbdf
Show file tree
Hide file tree
Showing 2 changed files with 57 additions and 13 deletions.
2 changes: 2 additions & 0 deletions include/linux/swap.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -260,6 +260,7 @@ struct swap_cluster_info {
#define CLUSTER_FLAG_FREE 1 /* This cluster is free */
#define CLUSTER_FLAG_NONFULL 2 /* This cluster is on nonfull list */
#define CLUSTER_FLAG_FRAG 4 /* This cluster is on nonfull list */
#define CLUSTER_FLAG_FULL 8 /* This cluster is on full list */

/*
* The first page in the swap file is the swap header, which is always marked
Expand Down Expand Up @@ -297,6 +298,7 @@ struct swap_info_struct {
unsigned char *swap_map; /* vmalloc'ed array of usage counts */
struct swap_cluster_info *cluster_info; /* cluster info. Only for SSD */
struct list_head free_clusters; /* free clusters list */
struct list_head full_clusters; /* full clusters list */
struct list_head nonfull_clusters[SWAP_NR_ORDERS];
/* list of cluster that contains at least one free slot */
struct list_head frag_clusters[SWAP_NR_ORDERS];
Expand Down
68 changes: 55 additions & 13 deletions mm/swapfile.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -440,10 +440,7 @@ static void swap_cluster_schedule_discard(struct swap_info_struct *si,
SWAP_MAP_BAD, SWAPFILE_CLUSTER);

VM_BUG_ON(ci->flags & CLUSTER_FLAG_FREE);
if (ci->flags & CLUSTER_FLAG_NONFULL)
list_move_tail(&ci->list, &si->discard_clusters);
else
list_add_tail(&ci->list, &si->discard_clusters);
list_move_tail(&ci->list, &si->discard_clusters);
ci->flags = 0;
schedule_work(&si->discard_work);
}
Expand All @@ -453,7 +450,7 @@ static void __free_cluster(struct swap_info_struct *si, struct swap_cluster_info
lockdep_assert_held(&si->lock);
lockdep_assert_held(&ci->lock);

if (ci->flags & CLUSTER_FLAG_NONFULL)
if (ci->flags)
list_move_tail(&ci->list, &si->free_clusters);
else
list_add_tail(&ci->list, &si->free_clusters);
Expand All @@ -480,7 +477,6 @@ static void swap_do_scheduled_discard(struct swap_info_struct *si)
SWAPFILE_CLUSTER);

spin_lock(&si->lock);

spin_lock(&ci->lock);
__free_cluster(si, ci);
memset(si->swap_map + idx * SWAPFILE_CLUSTER,
Expand Down Expand Up @@ -576,12 +572,9 @@ static void dec_cluster_info_page(struct swap_info_struct *p,

if (!(ci->flags & CLUSTER_FLAG_NONFULL)) {
VM_BUG_ON(ci->flags & CLUSTER_FLAG_FREE);
if (ci->flags & CLUSTER_FLAG_FRAG) {
if (ci->flags & CLUSTER_FLAG_FRAG)
p->frag_cluster_nr[ci->order]--;
list_move_tail(&ci->list, &p->nonfull_clusters[ci->order]);
} else {
list_add_tail(&ci->list, &p->nonfull_clusters[ci->order]);
}
list_move_tail(&ci->list, &p->nonfull_clusters[ci->order]);
ci->flags = CLUSTER_FLAG_NONFULL;
}
}
Expand Down Expand Up @@ -674,8 +667,8 @@ static void cluster_alloc_range(struct swap_info_struct *si, struct swap_cluster
(CLUSTER_FLAG_FREE | CLUSTER_FLAG_NONFULL | CLUSTER_FLAG_FRAG)));
if (ci->flags & CLUSTER_FLAG_FRAG)
si->frag_cluster_nr[ci->order]--;
list_del(&ci->list);
ci->flags = 0;
list_move_tail(&ci->list, &si->full_clusters);
ci->flags = CLUSTER_FLAG_FULL;
}
}

Expand Down Expand Up @@ -718,6 +711,46 @@ static unsigned int alloc_swap_scan_cluster(struct swap_info_struct *si, unsigne
return offset;
}

static void swap_reclaim_full_clusters(struct swap_info_struct *si)
{
long to_scan = 1;
unsigned long offset, end;
struct swap_cluster_info *ci;
unsigned char *map = si->swap_map;
int nr_reclaim, total_reclaimed = 0;

if (atomic_long_read(&nr_swap_pages) <= SWAPFILE_CLUSTER)
to_scan = si->inuse_pages / SWAPFILE_CLUSTER;

while (!list_empty(&si->full_clusters)) {
ci = list_first_entry(&si->full_clusters, struct swap_cluster_info, list);
list_move_tail(&ci->list, &si->full_clusters);
offset = cluster_offset(si, ci);
end = min(si->max, offset + SWAPFILE_CLUSTER);
to_scan--;

while (offset < end) {
if (READ_ONCE(map[offset]) == SWAP_HAS_CACHE) {
spin_unlock(&si->lock);
nr_reclaim = __try_to_reclaim_swap(si, offset,
TTRS_ANYWAY | TTRS_DIRECT);
spin_lock(&si->lock);
if (nr_reclaim > 0) {
offset += nr_reclaim;
total_reclaimed += nr_reclaim;
continue;
} else if (nr_reclaim < 0) {
offset += -nr_reclaim;
continue;
}
}
offset++;
}
if (to_scan <= 0 || total_reclaimed)
break;
}
}

/*
* Try to get swap entries with specified order from current cpu's swap entry
* pool (a cluster). This might involve allocating a new cluster for current CPU
Expand Down Expand Up @@ -826,7 +859,15 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o
goto done;
}
}

done:
/* Try reclaim from full clusters if device is nearfull */
if (vm_swap_full() && (!found || (si->pages - si->inuse_pages) < SWAPFILE_CLUSTER)) {
swap_reclaim_full_clusters(si);
if (!found && !order && si->pages != si->inuse_pages)
goto new_cluster;
}

cluster->next[order] = offset;
return found;
}
Expand Down Expand Up @@ -3115,6 +3156,7 @@ static int setup_swap_map_and_extents(struct swap_info_struct *p,
nr_good_pages = maxpages - 1; /* omit header page */

INIT_LIST_HEAD(&p->free_clusters);
INIT_LIST_HEAD(&p->full_clusters);
INIT_LIST_HEAD(&p->discard_clusters);

for (i = 0; i < SWAP_NR_ORDERS; i++) {
Expand Down

0 comments on commit 2cacbdf

Please sign in to comment.