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Message-Id: <20240730-swap-allocator-v5-8-cb9c148b9297@kernel.org>
Date: Tue, 30 Jul 2024 23:49:20 -0700
From: chrisl@...nel.org
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Kairui Song <kasong@...cent.com>, Hugh Dickins <hughd@...gle.com>,
Ryan Roberts <ryan.roberts@....com>, "Huang, Ying" <ying.huang@...el.com>,
Kalesh Singh <kaleshsingh@...gle.com>, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, Chris Li <chrisl@...nel.org>,
Barry Song <baohua@...nel.org>
Subject: [PATCH v5 8/9] mm: swap: relaim the cached parts that got scanned
From: Kairui Song <kasong@...cent.com>
This commit implements reclaim during scan for cluster allocator.
Cluster scanning were unable to reuse SWAP_HAS_CACHE slots, which
could result in low allocation success rate or early OOM.
So to ensure maximum allocation success rate, integrate reclaiming
with scanning. If found a range of suitable swap slots but fragmented
due to HAS_CACHE, just try to reclaim the slots.
Signed-off-by: Kairui Song <kasong@...cent.com>
---
include/linux/swap.h | 1 +
mm/swapfile.c | 140 +++++++++++++++++++++++++++++++++++++++------------
2 files changed, 110 insertions(+), 31 deletions(-)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 5a14b6c65949..9eb740563d63 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -302,6 +302,7 @@ struct swap_info_struct {
/* list of cluster that contains at least one free slot */
struct list_head frag_clusters[SWAP_NR_ORDERS];
/* list of cluster that are fragmented or contented */
+ unsigned int frag_cluster_nr[SWAP_NR_ORDERS];
unsigned int lowest_bit; /* index of first free in swap_map */
unsigned int highest_bit; /* index of last free in swap_map */
unsigned int pages; /* total of usable pages of swap */
diff --git a/mm/swapfile.c b/mm/swapfile.c
index eb3e387e86b2..50e7f600a9a1 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -513,6 +513,10 @@ static void free_cluster(struct swap_info_struct *si, struct swap_cluster_info *
VM_BUG_ON(ci->count != 0);
lockdep_assert_held(&si->lock);
lockdep_assert_held(&ci->lock);
+
+ if (ci->flags & CLUSTER_FLAG_FRAG)
+ si->frag_cluster_nr[ci->order]--;
+
/*
* If the swap is discardable, prepare discard the cluster
* instead of free it immediately. The cluster will be freed
@@ -572,31 +576,84 @@ 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
+ } else {
list_add_tail(&ci->list, &p->nonfull_clusters[ci->order]);
+ }
ci->flags = CLUSTER_FLAG_NONFULL;
}
}
-static inline bool cluster_scan_range(struct swap_info_struct *si, unsigned int start,
- unsigned int nr_pages)
+static bool cluster_reclaim_range(struct swap_info_struct *si,
+ struct swap_cluster_info *ci,
+ unsigned long start, unsigned long end)
{
- unsigned char *p = si->swap_map + start;
- unsigned char *end = p + nr_pages;
+ unsigned char *map = si->swap_map;
+ unsigned long offset;
+
+ spin_unlock(&ci->lock);
+ spin_unlock(&si->lock);
+
+ for (offset = start; offset < end; offset++) {
+ switch (READ_ONCE(map[offset])) {
+ case 0:
+ continue;
+ case SWAP_HAS_CACHE:
+ if (__try_to_reclaim_swap(si, offset, TTRS_ANYWAY | TTRS_DIRECT) > 0)
+ continue;
+ goto out;
+ default:
+ goto out;
+ }
+ }
+out:
+ spin_lock(&si->lock);
+ spin_lock(&ci->lock);
- while (p < end)
- if (*p++)
+ /*
+ * Recheck the range no matter reclaim succeeded or not, the slot
+ * could have been be freed while we are not holding the lock.
+ */
+ for (offset = start; offset < end; offset++)
+ if (READ_ONCE(map[offset]))
return false;
return true;
}
+static bool cluster_scan_range(struct swap_info_struct *si,
+ struct swap_cluster_info *ci,
+ unsigned long start, unsigned int nr_pages)
+{
+ unsigned long offset, end = start + nr_pages;
+ unsigned char *map = si->swap_map;
+ bool need_reclaim = false;
-static inline void cluster_alloc_range(struct swap_info_struct *si, struct swap_cluster_info *ci,
- unsigned int start, unsigned char usage,
- unsigned int order)
+ for (offset = start; offset < end; offset++) {
+ switch (READ_ONCE(map[offset])) {
+ case 0:
+ continue;
+ case SWAP_HAS_CACHE:
+ if (!vm_swap_full())
+ return false;
+ need_reclaim = true;
+ continue;
+ default:
+ return false;
+ }
+ }
+
+ if (need_reclaim)
+ return cluster_reclaim_range(si, ci, start, end);
+
+ return true;
+}
+
+static void cluster_alloc_range(struct swap_info_struct *si, struct swap_cluster_info *ci,
+ unsigned int start, unsigned char usage,
+ unsigned int order)
{
unsigned int nr_pages = 1 << order;
@@ -615,6 +672,8 @@ static inline void cluster_alloc_range(struct swap_info_struct *si, struct swap_
if (ci->count == SWAPFILE_CLUSTER) {
VM_BUG_ON(!(ci->flags &
(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;
}
@@ -640,7 +699,7 @@ static unsigned int alloc_swap_scan_cluster(struct swap_info_struct *si, unsigne
}
while (offset <= end) {
- if (cluster_scan_range(si, offset, nr_pages)) {
+ if (cluster_scan_range(si, ci, offset, nr_pages)) {
cluster_alloc_range(si, ci, offset, usage, order);
*foundp = offset;
if (ci->count == SWAPFILE_CLUSTER) {
@@ -668,9 +727,8 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o
unsigned char usage)
{
struct percpu_cluster *cluster;
- struct swap_cluster_info *ci, *n;
+ struct swap_cluster_info *ci;
unsigned int offset, found = 0;
- LIST_HEAD(fraged);
new_cluster:
lockdep_assert_held(&si->lock);
@@ -690,25 +748,42 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o
}
if (order < PMD_ORDER) {
- list_for_each_entry_safe(ci, n, &si->nonfull_clusters[order], list) {
- list_move_tail(&ci->list, &fraged);
+ unsigned int frags = 0;
+
+ while (!list_empty(&si->nonfull_clusters[order])) {
+ ci = list_first_entry(&si->nonfull_clusters[order],
+ struct swap_cluster_info, list);
+ list_move_tail(&ci->list, &si->frag_clusters[order]);
ci->flags = CLUSTER_FLAG_FRAG;
+ si->frag_cluster_nr[order]++;
offset = alloc_swap_scan_cluster(si, cluster_offset(si, ci),
&found, order, usage);
+ frags++;
if (found)
break;
}
if (!found) {
- list_for_each_entry_safe(ci, n, &si->frag_clusters[order], list) {
+ /*
+ * Nonfull clusters are moved to frag tail if we reached
+ * here, count them too, don't over scan the frag list.
+ */
+ while (frags < si->frag_cluster_nr[order]) {
+ ci = list_first_entry(&si->frag_clusters[order],
+ struct swap_cluster_info, list);
+ /*
+ * Rotate the frag list to iterate, they were all failing
+ * high order allocation or moved here due to per-CPU usage,
+ * this help keeping usable cluster ahead.
+ */
+ list_move_tail(&ci->list, &si->frag_clusters[order]);
offset = alloc_swap_scan_cluster(si, cluster_offset(si, ci),
&found, order, usage);
+ frags++;
if (found)
break;
}
}
-
- list_splice_tail(&fraged, &si->frag_clusters[order]);
}
if (found)
@@ -729,25 +804,28 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o
/* Order 0 stealing from higher order */
for (int o = 1; o < PMD_ORDER; o++) {
- if (!list_empty(&si->frag_clusters[o])) {
+ /*
+ * Clusters here have at least one usable slots and can't fail order 0
+ * allocation, but reclaim may drop si->lock and race with another user.
+ */
+ while (!list_empty(&si->frag_clusters[o])) {
ci = list_first_entry(&si->frag_clusters[o],
struct swap_cluster_info, list);
- offset = alloc_swap_scan_cluster(si, cluster_offset(si, ci), &found,
- 0, usage);
- VM_BUG_ON(!found);
- goto done;
+ offset = alloc_swap_scan_cluster(si, cluster_offset(si, ci),
+ &found, 0, usage);
+ if (found)
+ goto done;
}
- if (!list_empty(&si->nonfull_clusters[o])) {
- ci = list_first_entry(&si->nonfull_clusters[o], struct swap_cluster_info,
- list);
+ while (!list_empty(&si->nonfull_clusters[o])) {
+ ci = list_first_entry(&si->nonfull_clusters[o],
+ struct swap_cluster_info, list);
offset = alloc_swap_scan_cluster(si, cluster_offset(si, ci),
&found, 0, usage);
- VM_BUG_ON(!found);
- goto done;
+ if (found)
+ goto done;
}
}
-
done:
cluster->next[order] = offset;
return found;
@@ -3053,6 +3131,7 @@ static int setup_swap_map_and_extents(struct swap_info_struct *p,
for (i = 0; i < SWAP_NR_ORDERS; i++) {
INIT_LIST_HEAD(&p->nonfull_clusters[i]);
INIT_LIST_HEAD(&p->frag_clusters[i]);
+ p->frag_cluster_nr[i] = 0;
}
for (i = 0; i < swap_header->info.nr_badpages; i++) {
@@ -3096,7 +3175,6 @@ static int setup_swap_map_and_extents(struct swap_info_struct *p,
if (!cluster_info)
return nr_extents;
-
/*
* Reduce false cache line sharing between cluster_info and
* sharing same address space.
--
2.46.0.rc1.232.g9752f9e123-goog
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