Now that we no longer have a convenient flag in the cluster to determine
if a folio is large, free_swap_and_cache() will take a reference and
lock a large folio much more often, which could lead to contention and
(e.g.) failure to split large folios, etc.
Let's solve that problem by batch freeing swap and cache with a new
function, free_swap_and_cache_nr(), to free a contiguous range of swap
entries together. This allows us to first drop a reference to each swap
slot before we try to release the cache folio. This means we only try to
release the folio once, only taking the reference and lock once - much
better than the previous 512 times for the 2M THP case.
Contiguous swap entries are gathered in zap_pte_range() and
madvise_free_pte_range() in a similar way to how present ptes are
already gathered in zap_pte_range().
While we are at it, let's simplify by converting the return type of both
functions to void. The return value was used only by zap_pte_range() to
print a bad pte, and was ignored by everyone else, so the extra
reporting wasn't exactly guaranteed. We will still get the warning with
most of the information from get_swap_device(). With the batch version,
we wouldn't know which pte was bad anyway so could print the wrong one.
Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
---
include/linux/pgtable.h | 29 ++++++++++++
include/linux/swap.h | 12 +++--
mm/internal.h | 63 ++++++++++++++++++++++++++
mm/madvise.c | 12 +++--
mm/memory.c | 13 +++---
mm/swapfile.c | 97 +++++++++++++++++++++++++++++++++--------
6 files changed, 195 insertions(+), 31 deletions(-)
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index a3fc8150b047..75096025fe52 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -708,6 +708,35 @@ static inline void pte_clear_not_present_full(struct mm_struct *mm,
}
#endif
+#ifndef clear_not_present_full_ptes
+/**
+ * clear_not_present_full_ptes - Clear multiple not present PTEs which are
+ * consecutive in the pgtable.
+ * @mm: Address space the ptes represent.
+ * @addr: Address of the first pte.
+ * @ptep: Page table pointer for the first entry.
+ * @nr: Number of entries to clear.
+ * @full: Whether we are clearing a full mm.
+ *
+ * May be overridden by the architecture; otherwise, implemented as a simple
+ * loop over pte_clear_not_present_full().
+ *
+ * Context: The caller holds the page table lock. The PTEs are all not present.
+ * The PTEs are all in the same PMD.
+ */
+static inline void clear_not_present_full_ptes(struct mm_struct *mm,
+ unsigned long addr, pte_t *ptep, unsigned int nr, int full)
+{
+ for (;;) {
+ pte_clear_not_present_full(mm, addr, ptep, full);
+ if (--nr == 0)
+ break;
+ ptep++;
+ addr += PAGE_SIZE;
+ }
+}
+#endif
+
#ifndef __HAVE_ARCH_PTEP_CLEAR_FLUSH
extern pte_t ptep_clear_flush(struct vm_area_struct *vma,
unsigned long address,
diff --git a/include/linux/swap.h b/include/linux/swap.h
index f6f78198f000..5737236dc3ce 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -471,7 +471,7 @@ extern int swap_duplicate(swp_entry_t);
extern int swapcache_prepare(swp_entry_t);
extern void swap_free(swp_entry_t);
extern void swapcache_free_entries(swp_entry_t *entries, int n);
-extern int free_swap_and_cache(swp_entry_t);
+extern void free_swap_and_cache_nr(swp_entry_t entry, int nr);
int swap_type_of(dev_t device, sector_t offset);
int find_first_swap(dev_t *device);
extern unsigned int count_swap_pages(int, int);
@@ -520,8 +520,9 @@ static inline void put_swap_device(struct swap_info_struct *si)
#define free_pages_and_swap_cache(pages, nr) \
release_pages((pages), (nr));
-/* used to sanity check ptes in zap_pte_range when CONFIG_SWAP=0 */
-#define free_swap_and_cache(e) is_pfn_swap_entry(e)
+static inline void free_swap_and_cache_nr(swp_entry_t entry, int nr)
+{
+}
static inline void free_swap_cache(struct folio *folio)
{
@@ -589,6 +590,11 @@ static inline int add_swap_extent(struct swap_info_struct *sis,
}
#endif /* CONFIG_SWAP */
+static inline void free_swap_and_cache(swp_entry_t entry)
+{
+ free_swap_and_cache_nr(entry, 1);
+}
+
#ifdef CONFIG_MEMCG
static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg)
{
diff --git a/mm/internal.h b/mm/internal.h
index 3bdc8693b54f..de68705624b0 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -11,6 +11,8 @@
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/rmap.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>
#include <linux/tracepoint-defs.h>
struct folio_batch;
@@ -189,6 +191,67 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr,
return min(ptep - start_ptep, max_nr);
}
+
+/**
+ * pte_next_swp_offset - Increment the swap entry offset field of a swap pte.
+ * @pte: The initial pte state; is_swap_pte(pte) must be true.
+ *
+ * Increments the swap offset, while maintaining all other fields, including
+ * swap type, and any swp pte bits. The resulting pte is returned.
+ */
+static inline pte_t pte_next_swp_offset(pte_t pte)
+{
+ swp_entry_t entry = pte_to_swp_entry(pte);
+ pte_t new = __swp_entry_to_pte(__swp_entry(swp_type(entry),
+ swp_offset(entry) + 1));
+
+ if (pte_swp_soft_dirty(pte))
+ new = pte_swp_mksoft_dirty(new);
+ if (pte_swp_exclusive(pte))
+ new = pte_swp_mkexclusive(new);
+ if (pte_swp_uffd_wp(pte))
+ new = pte_swp_mkuffd_wp(new);
