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Message-Id: <20240403114032.1162100-2-ryan.roberts@arm.com>
Date: Wed, 3 Apr 2024 12:40:27 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: Andrew Morton <akpm@...ux-foundation.org>,
David Hildenbrand <david@...hat.com>,
Matthew Wilcox <willy@...radead.org>,
Huang Ying <ying.huang@...el.com>,
Gao Xiang <xiang@...nel.org>,
Yu Zhao <yuzhao@...gle.com>,
Yang Shi <shy828301@...il.com>,
Michal Hocko <mhocko@...e.com>,
Kefeng Wang <wangkefeng.wang@...wei.com>,
Barry Song <21cnbao@...il.com>,
Chris Li <chrisl@...nel.org>,
Lance Yang <ioworker0@...il.com>
Cc: Ryan Roberts <ryan.roberts@....com>,
linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: [PATCH v6 1/6] mm: swap: Remove CLUSTER_FLAG_HUGE from swap_cluster_info:flags
As preparation for supporting small-sized THP in the swap-out path,
without first needing to split to order-0, Remove the CLUSTER_FLAG_HUGE,
which, when present, always implies PMD-sized THP, which is the same as
the cluster size.
The only use of the flag was to determine whether a swap entry refers to
a single page or a PMD-sized THP in swap_page_trans_huge_swapped().
Instead of relying on the flag, we now pass in nr_pages, which
originates from the folio's number of pages. This allows the logic to
work for folios of any order.
The one snag is that one of the swap_page_trans_huge_swapped() call
sites does not have the folio. But it was only being called there to
shortcut a call __try_to_reclaim_swap() in some cases.
__try_to_reclaim_swap() gets the folio and (via some other functions)
calls swap_page_trans_huge_swapped(). So I've removed the problematic
call site and believe the new logic should be functionally equivalent.
That said, removing the fast path means that we will take a reference
and trylock a large folio much more often, which we would like to avoid.
The next patch will solve this.
Removing CLUSTER_FLAG_HUGE also means we can remove split_swap_cluster()
which used to be called during folio splitting, since
split_swap_cluster()'s only job was to remove the flag.
Reviewed-by: "Huang, Ying" <ying.huang@...el.com>
Signed-off-by: Ryan Roberts <ryan.roberts@....com>
---
include/linux/swap.h | 10 ----------
mm/huge_memory.c | 3 ---
mm/swapfile.c | 47 ++++++++------------------------------------
3 files changed, 8 insertions(+), 52 deletions(-)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index a211a0383425..f6f78198f000 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -259,7 +259,6 @@ struct swap_cluster_info {
};
#define CLUSTER_FLAG_FREE 1 /* This cluster is free */
#define CLUSTER_FLAG_NEXT_NULL 2 /* This cluster has no next cluster */
-#define CLUSTER_FLAG_HUGE 4 /* This cluster is backing a transparent huge page */
/*
* We assign a cluster to each CPU, so each CPU can allocate swap entry from
@@ -590,15 +589,6 @@ static inline int add_swap_extent(struct swap_info_struct *sis,
}
#endif /* CONFIG_SWAP */
-#ifdef CONFIG_THP_SWAP
-extern int split_swap_cluster(swp_entry_t entry);
-#else
-static inline int split_swap_cluster(swp_entry_t entry)
-{
- return 0;
-}
-#endif
-
#ifdef CONFIG_MEMCG
static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg)
{
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index ea6d1f09a0b9..3ca9282a0dc9 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2844,9 +2844,6 @@ static void __split_huge_page(struct page *page, struct list_head *list,
shmem_uncharge(folio->mapping->host, nr_dropped);
remap_page(folio, nr);
- if (folio_test_swapcache(folio))
- split_swap_cluster(folio->swap);
-
/*
* set page to its compound_head when split to non order-0 pages, so
* we can skip unlocking it below, since PG_locked is transferred to
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 5e6d2304a2a4..0d44ee2b4f9c 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -343,18 +343,6 @@ static inline void cluster_set_null(struct swap_cluster_info *info)
info->data = 0;
}
-static inline bool cluster_is_huge(struct swap_cluster_info *info)
-{
- if (IS_ENABLED(CONFIG_THP_SWAP))
- return info->flags & CLUSTER_FLAG_HUGE;
- return false;
-}
-
-static inline void cluster_clear_huge(struct swap_cluster_info *info)
-{
- info->flags &= ~CLUSTER_FLAG_HUGE;
-}
-
static inline struct swap_cluster_info *lock_cluster(struct swap_info_struct *si,
unsigned long offset)
{
@@ -1027,7 +1015,7 @@ static int swap_alloc_cluster(struct swap_info_struct *si, swp_entry_t *slot)
offset = idx * SWAPFILE_CLUSTER;
ci = lock_cluster(si, offset);
alloc_cluster(si, idx);
- cluster_set_count_flag(ci, SWAPFILE_CLUSTER, CLUSTER_FLAG_HUGE);
+ cluster_set_count(ci, SWAPFILE_CLUSTER);
memset(si->swap_map + offset, SWAP_HAS_CACHE, SWAPFILE_CLUSTER);
unlock_cluster(ci);
@@ -1365,7 +1353,6 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry)
ci = lock_cluster_or_swap_info(si, offset);
if (size == SWAPFILE_CLUSTER) {
- VM_BUG_ON(!cluster_is_huge(ci));
map = si->swap_map + offset;
for (i = 0; i < SWAPFILE_CLUSTER; i++) {
val = map[i];
@@ -1373,7 +1360,6 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry)
if (val == SWAP_HAS_CACHE)
free_entries++;
}
- cluster_clear_huge(ci);
if (free_entries == SWAPFILE_CLUSTER) {
unlock_cluster_or_swap_info(si, ci);
spin_lock(&si->lock);
@@ -1395,23 +1381,6 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry)
unlock_cluster_or_swap_info(si, ci);
}
-#ifdef CONFIG_THP_SWAP
-int split_swap_cluster(swp_entry_t entry)
-{
- struct swap_info_struct *si;
- struct swap_cluster_info *ci;
- unsigned long offset = swp_offset(entry);
-
- si = _swap_info_get(entry);
- if (!si)
- return -EBUSY;
- ci = lock_cluster(si, offset);
- cluster_clear_huge(ci);
- unlock_cluster(ci);
- return 0;
-}
-#endif
-
static int swp_entry_cmp(const void *ent1, const void *ent2)
{
const swp_entry_t *e1 = ent1, *e2 = ent2;
@@ -1519,22 +1488,23 @@ int swp_swapcount(swp_entry_t entry)
}
static bool swap_page_trans_huge_swapped(struct swap_info_struct *si,
- swp_entry_t entry)
+ swp_entry_t entry,
+ unsigned int nr_pages)
{
struct swap_cluster_info *ci;
unsigned char *map = si->swap_map;
unsigned long roffset = swp_offset(entry);
- unsigned long offset = round_down(roffset, SWAPFILE_CLUSTER);
+ unsigned long offset = round_down(roffset, nr_pages);
int i;
bool ret = false;
ci = lock_cluster_or_swap_info(si, offset);
- if (!ci || !cluster_is_huge(ci)) {
+ if (!ci || nr_pages == 1) {
if (swap_count(map[roffset]))
ret = true;
goto unlock_out;
}
- for (i = 0; i < SWAPFILE_CLUSTER; i++) {
+ for (i = 0; i < nr_pages; i++) {
if (swap_count(map[offset + i])) {
ret = true;
break;
@@ -1556,7 +1526,7 @@ static bool folio_swapped(struct folio *folio)
if (!IS_ENABLED(CONFIG_THP_SWAP) || likely(!folio_test_large(folio)))
return swap_swapcount(si, entry) != 0;
- return swap_page_trans_huge_swapped(si, entry);
+ return swap_page_trans_huge_swapped(si, entry, folio_nr_pages(folio));
}
/**
@@ -1622,8 +1592,7 @@ int free_swap_and_cache(swp_entry_t entry)
}
count = __swap_entry_free(p, entry);
- if (count == SWAP_HAS_CACHE &&
- !swap_page_trans_huge_swapped(p, entry))
+ if (count == SWAP_HAS_CACHE)
__try_to_reclaim_swap(p, swp_offset(entry),
TTRS_UNMAPPED | TTRS_FULL);
put_swap_device(p);
--
2.25.1
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