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Subject[PATCH -mm 12/21] mm, THP, swap: Support PMD swap mapping in swapoff
Date
From: Huang Ying <ying.huang@intel.com>

During swapoff, for a huge swap cluster, we need to allocate a THP,
read its contents into the THP and unuse the PMD and PTE swap mappings
to it. If failed to allocate a THP, the huge swap cluster will be
split.

During unuse, if it is found that the swap cluster mapped by a PMD
swap mapping is split already, we will split the PMD swap mapping and
unuse the PTEs.

Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Shaohua Li <shli@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Zi Yan <zi.yan@cs.rutgers.edu>
---
include/asm-generic/pgtable.h | 15 ++----
include/linux/huge_mm.h | 8 ++++
mm/huge_memory.c | 4 +-
mm/swapfile.c | 86 ++++++++++++++++++++++++++++++++++-
4 files changed, 98 insertions(+), 15 deletions(-)

diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index bb8354981a36..caa381962cd2 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -931,22 +931,13 @@ static inline int pmd_none_or_trans_huge_or_clear_bad(pmd_t *pmd)
barrier();
#endif
/*
- * !pmd_present() checks for pmd migration entries
- *
- * The complete check uses is_pmd_migration_entry() in linux/swapops.h
- * But using that requires moving current function and pmd_trans_unstable()
- * to linux/swapops.h to resovle dependency, which is too much code move.
- *
- * !pmd_present() is equivalent to is_pmd_migration_entry() currently,
- * because !pmd_present() pages can only be under migration not swapped
- * out.
- *
- * pmd_none() is preseved for future condition checks on pmd migration
+ * pmd_none() is preseved for future condition checks on pmd swap
* entries and not confusing with this function name, although it is
* redundant with !pmd_present().
*/
if (pmd_none(pmdval) || pmd_trans_huge(pmdval) ||
- (IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION) && !pmd_present(pmdval)))
+ ((IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION) ||
+ IS_ENABLED(CONFIG_THP_SWAP)) && !pmd_present(pmdval)))
return 1;
if (unlikely(pmd_bad(pmdval))) {
pmd_clear_bad(pmd);
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 1cfd43047f0d..4e299e327720 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -405,6 +405,8 @@ static inline gfp_t alloc_hugepage_direct_gfpmask(struct vm_area_struct *vma)
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */

#ifdef CONFIG_THP_SWAP
+extern int split_huge_swap_pmd(struct vm_area_struct *vma, pmd_t *pmd,
+ unsigned long address, pmd_t orig_pmd);
extern int do_huge_pmd_swap_page(struct vm_fault *vmf, pmd_t orig_pmd);

static inline bool transparent_hugepage_swapin_enabled(
@@ -430,6 +432,12 @@ static inline bool transparent_hugepage_swapin_enabled(
return false;
}
#else /* CONFIG_THP_SWAP */
+static inline int split_huge_swap_pmd(struct vm_area_struct *vma, pmd_t *pmd,
+ unsigned long address, pmd_t orig_pmd)
+{
+ return 0;
+}
+
static inline int do_huge_pmd_swap_page(struct vm_fault *vmf, pmd_t orig_pmd)
{
return 0;
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 0538fe48918b..445c5416d251 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1666,8 +1666,8 @@ static void __split_huge_swap_pmd(struct vm_area_struct *vma,
pmd_populate(mm, pmd, pgtable);
}

-static int split_huge_swap_pmd(struct vm_area_struct *vma, pmd_t *pmd,
- unsigned long address, pmd_t orig_pmd)
+int split_huge_swap_pmd(struct vm_area_struct *vma, pmd_t *pmd,
+ unsigned long address, pmd_t orig_pmd)
{
struct mm_struct *mm = vma->vm_mm;
spinlock_t *ptl;
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 3bac299a1b25..9599c7059539 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1937,6 +1937,11 @@ static inline int pte_same_as_swp(pte_t pte, pte_t swp_pte)
return pte_same(pte_swp_clear_soft_dirty(pte), swp_pte);
}

+static inline int pmd_same_as_swp(pmd_t pmd, pmd_t swp_pmd)
+{
+ return pmd_same(pmd_swp_clear_soft_dirty(pmd), swp_pmd);
+}
+
/*
* No need to decide whether this PTE shares the swap entry with others,
* just let do_wp_page work it out if a write is requested later - to
@@ -1998,6 +2003,57 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
return ret;
}

+#ifdef CONFIG_THP_SWAP
+static int unuse_pmd(struct vm_area_struct *vma, pmd_t *pmd,
+ unsigned long addr, swp_entry_t entry, struct page *page)
+{
+ struct mem_cgroup *memcg;
+ struct swap_info_struct *si;
+ spinlock_t *ptl;
+ int ret = 1;
+
+ if (mem_cgroup_try_charge(page, vma->vm_mm, GFP_KERNEL,
+ &memcg, true)) {
+ ret = -ENOMEM;
+ goto out_nolock;
+ }
+
+ ptl = pmd_lock(vma->vm_mm, pmd);
+ if (unlikely(!pmd_same_as_swp(*pmd, swp_entry_to_pmd(entry)))) {
+ mem_cgroup_cancel_charge(page, memcg, true);
+ ret = 0;
+ goto out;
+ }
+
+ add_mm_counter(vma->vm_mm, MM_SWAPENTS, -HPAGE_PMD_NR);
+ add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
+ get_page(page);
+ set_pmd_at(vma->vm_mm, addr, pmd,
+ pmd_mkold(mk_huge_pmd(page, vma->vm_page_prot)));
+ page_add_anon_rmap(page, vma, addr, true);
+ mem_cgroup_commit_charge(page, memcg, true, true);
+ si = _swap_info_get(entry);
+ if (si)
+ swap_free_cluster(si, entry);
+ /*
+ * Move the page to the active list so it is not
+ * immediately swapped out again after swapon.
+ */
+ activate_page(page);
+out:
+ spin_unlock(ptl);
+out_nolock:
+ return ret;
+}
+#else
+static inline int unuse_pmd(struct vm_area_struct *vma, pmd_t *pmd,
+ unsigned long addr, swp_entry_t entry,
+ struct page *page)
+{
+ return 0;
+}
+#endif
+
static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
unsigned long addr, unsigned long end,
swp_entry_t entry, struct page *page)
@@ -2038,7 +2094,7 @@ static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
unsigned long addr, unsigned long end,
swp_entry_t entry, struct page *page)
{
- pmd_t *pmd;
+ pmd_t swp_pmd = swp_entry_to_pmd(entry), *pmd, orig_pmd;
unsigned long next;
int ret;

@@ -2046,6 +2102,24 @@ static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
do {
cond_resched();
next = pmd_addr_end(addr, end);
+ orig_pmd = *pmd;
+ if (thp_swap_supported() && is_swap_pmd(orig_pmd)) {
+ if (likely(!pmd_same_as_swp(orig_pmd, swp_pmd)))
+ continue;
+ /* Huge cluster has been split already */
+ if (!PageTransCompound(page)) {
+ ret = split_huge_swap_pmd(vma, pmd,
+ addr, orig_pmd);
+ if (ret)
+ return ret;
+ ret = unuse_pte_range(vma, pmd, addr,
+ next, entry, page);
+ } else
+ ret = unuse_pmd(vma, pmd, addr, entry, page);
+ if (ret)
+ return ret;
+ continue;
+ }
if (pmd_none_or_trans_huge_or_clear_bad(pmd))
continue;
ret = unuse_pte_range(vma, pmd, addr, next, entry, page);
@@ -2210,6 +2284,7 @@ int try_to_unuse(unsigned int type, bool frontswap,
* to prevent compiler doing
* something odd.
*/
+ struct swap_cluster_info *ci = NULL;
unsigned char swcount;
struct page *page;
swp_entry_t entry;
@@ -2239,6 +2314,7 @@ int try_to_unuse(unsigned int type, bool frontswap,
* there are races when an instance of an entry might be missed.
*/
while ((i = find_next_to_unuse(si, i, frontswap)) != 0) {
+retry:
if (signal_pending(current)) {
retval = -EINTR;
break;
@@ -2250,6 +2326,8 @@ int try_to_unuse(unsigned int type, bool frontswap,
* page and read the swap into it.
*/
swap_map = &si->swap_map[i];
+ if (si->cluster_info)
+ ci = si->cluster_info + i / SWAPFILE_CLUSTER;
entry = swp_entry(type, i);
page = read_swap_cache_async(entry,
GFP_HIGHUSER_MOVABLE, NULL, 0, false);
@@ -2270,6 +2348,12 @@ int try_to_unuse(unsigned int type, bool frontswap,
*/
if (!swcount || swcount == SWAP_MAP_BAD)
continue;
+ /* Split huge cluster if failed to allocate huge page */
+ if (thp_swap_supported() && cluster_is_huge(ci)) {
+ retval = split_swap_cluster(entry, false);
+ if (!retval || retval == -EEXIST)
+ goto retry;
+ }
retval = -ENOMEM;
break;
}
--
2.17.0
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