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Subject[PATCH v4 1/2] mm: Refactor swap-in logic out of shmem_getpage_gfp
Date
swap-in logic could be reused independently without rest of the logic
in shmem_getpage_gfp. So lets refactor it out as an independent
function.

Signed-off-by: Vineeth Remanan Pillai <vpillai@digitalocean.com>
---
mm/shmem.c | 449 +++++++++++++++++++++++++++++------------------------
1 file changed, 244 insertions(+), 205 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 6ece1e2fe76e..7cd7ee69f670 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -123,6 +123,10 @@ static unsigned long shmem_default_max_inodes(void)
static bool shmem_should_replace_page(struct page *page, gfp_t gfp);
static int shmem_replace_page(struct page **pagep, gfp_t gfp,
struct shmem_inode_info *info, pgoff_t index);
+static int shmem_swapin_page(struct inode *inode, pgoff_t index,
+ struct page **pagep, enum sgp_type sgp,
+ gfp_t gfp, struct vm_area_struct *vma,
+ vm_fault_t *fault_type);
static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
struct page **pagep, enum sgp_type sgp,
gfp_t gfp, struct vm_area_struct *vma,
@@ -1575,6 +1579,116 @@ static int shmem_replace_page(struct page **pagep, gfp_t gfp,
return error;
}

+/*
+ * Swap in the page pointed to by *pagep.
+ * Caller has to make sure that *pagep contains a valid swapped page.
+ * Returns 0 and the page in pagep if success. On failure, returns the
+ * the error code and NULL in *pagep.
+ */
+static int shmem_swapin_page(struct inode *inode, pgoff_t index,
+ struct page **pagep, enum sgp_type sgp,
+ gfp_t gfp, struct vm_area_struct *vma,
+ vm_fault_t *fault_type)
+{
+ struct address_space *mapping = inode->i_mapping;
+ struct shmem_inode_info *info = SHMEM_I(inode);
+ struct mm_struct *charge_mm = vma ? vma->vm_mm : current->mm;
+ struct mem_cgroup *memcg;
+ struct page *page;
+ swp_entry_t swap;
+ int error;
+
+ VM_BUG_ON(!*pagep || !xa_is_value(*pagep));
+ swap = radix_to_swp_entry(*pagep);
+ *pagep = NULL;
+
+ /* Look it up and read it in.. */
+ page = lookup_swap_cache(swap, NULL, 0);
+ if (!page) {
+ /* Or update major stats only when swapin succeeds?? */
+ if (fault_type) {
+ *fault_type |= VM_FAULT_MAJOR;
+ count_vm_event(PGMAJFAULT);
+ count_memcg_event_mm(charge_mm, PGMAJFAULT);
+ }
+ /* Here we actually start the io */
+ page = shmem_swapin(swap, gfp, info, index);
+ if (!page) {
+ error = -ENOMEM;
+ goto failed;
+ }
+ }
+
+ /* We have to do this with page locked to prevent races */
+ lock_page(page);
+ if (!PageSwapCache(page) || page_private(page) != swap.val ||
+ !shmem_confirm_swap(mapping, index, swap)) {
+ error = -EEXIST;
+ goto unlock;
+ }
+ if (!PageUptodate(page)) {
+ error = -EIO;
+ goto failed;
+ }
+ wait_on_page_writeback(page);
+
+ if (shmem_should_replace_page(page, gfp)) {
+ error = shmem_replace_page(&page, gfp, info, index);
+ if (error)
+ goto failed;
+ }
+
+ error = mem_cgroup_try_charge_delay(page, charge_mm, gfp, &memcg,
+ false);
+ if (!error) {
+ error = shmem_add_to_page_cache(page, mapping, index,
+ swp_to_radix_entry(swap), gfp);
+ /*
+ * We already confirmed swap under page lock, and make
+ * no memory allocation here, so usually no possibility
+ * of error; but free_swap_and_cache() only trylocks a
+ * page, so it is just possible that the entry has been
+ * truncated or holepunched since swap was confirmed.
+ * shmem_undo_range() will have done some of the
+ * unaccounting, now delete_from_swap_cache() will do
+ * the rest.
+ */
+ if (error) {
+ mem_cgroup_cancel_charge(page, memcg, false);
+ delete_from_swap_cache(page);
+ }
+ }
+ if (error)
+ goto failed;
+
+ mem_cgroup_commit_charge(page, memcg, true, false);
+
+ spin_lock_irq(&info->lock);
+ info->swapped--;
+ shmem_recalc_inode(inode);
+ spin_unlock_irq(&info->lock);
+
+ if (sgp == SGP_WRITE)
+ mark_page_accessed(page);
+
+ delete_from_swap_cache(page);
+ set_page_dirty(page);
+ swap_free(swap);
+
+ *pagep = page;
+ return 0;
+failed:
+ if (!shmem_confirm_swap(mapping, index, swap))
+ error = -EEXIST;
+unlock:
+ if (page) {
+ unlock_page(page);
+ put_page(page);
+ }
+
+ return error;
+}
+
/*
* shmem_getpage_gfp - find page in cache, or get from swap, or allocate
*
@@ -1596,7 +1710,6 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
struct mm_struct *charge_mm;
struct mem_cgroup *memcg;
struct page *page;
- swp_entry_t swap;
enum sgp_type sgp_huge = sgp;
pgoff_t hindex = index;
int error;
@@ -1608,17 +1721,23 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
if (sgp == SGP_NOHUGE || sgp == SGP_HUGE)
sgp = SGP_CACHE;
repeat:
- swap.val = 0;
+ if (sgp <= SGP_CACHE &&
+ ((loff_t)index << PAGE_SHIFT) >= i_size_read(inode)) {
+ return -EINVAL;
+ }
+
+ sbinfo = SHMEM_SB(inode->i_sb);
+ charge_mm = vma ? vma->vm_mm : current->mm;
+
page = find_lock_entry(mapping, index);
if (xa_is_value(page)) {
- swap = radix_to_swp_entry(page);
- page = NULL;
- }
+ error = shmem_swapin_page(inode, index, &page,
+ sgp, gfp, vma, fault_type);
+ if (error == -EEXIST)
+ goto repeat;

- if (sgp <= SGP_CACHE &&
- ((loff_t)index << PAGE_SHIFT) >= i_size_read(inode)) {
- error = -EINVAL;
- goto unlock;
+ *pagep = page;
+ return error;
}

if (page && sgp == SGP_WRITE)
@@ -1632,7 +1751,7 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
put_page(page);
page = NULL;
}
- if (page || (sgp == SGP_READ && !swap.val)) {
+ if (page || sgp == SGP_READ) {
*pagep = page;
return 0;
}
@@ -1641,215 +1760,138 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
* Fast cache lookup did not find it:
* bring it back from swap or allocate.
*/
- sbinfo = SHMEM_SB(inode->i_sb);
- charge_mm = vma ? vma->vm_mm : current->mm;
-
- if (swap.val) {
- /* Look it up and read it in.. */
- page = lookup_swap_cache(swap, NULL, 0);
- if (!page) {
- /* Or update major stats only when swapin succeeds?? */
- if (fault_type) {
- *fault_type |= VM_FAULT_MAJOR;
- count_vm_event(PGMAJFAULT);
- count_memcg_event_mm(charge_mm, PGMAJFAULT);
- }
- /* Here we actually start the io */
- page = shmem_swapin(swap, gfp, info, index);
- if (!page) {
- error = -ENOMEM;
- goto failed;
- }
- }
-
- /* We have to do this with page locked to prevent races */
- lock_page(page);
- if (!PageSwapCache(page) || page_private(page) != swap.val ||
- !shmem_confirm_swap(mapping, index, swap)) {
- error = -EEXIST; /* try again */
- goto unlock;
- }
- if (!PageUptodate(page)) {
- error = -EIO;
- goto failed;
- }
- wait_on_page_writeback(page);
-
- if (shmem_should_replace_page(page, gfp)) {
- error = shmem_replace_page(&page, gfp, info, index);
- if (error)
- goto failed;
- }

- error = mem_cgroup_try_charge_delay(page, charge_mm, gfp, &memcg,
- false);
- if (!error) {
- error = shmem_add_to_page_cache(page, mapping, index,
- swp_to_radix_entry(swap), gfp);
- /*
- * We already confirmed swap under page lock, and make
- * no memory allocation here, so usually no possibility
- * of error; but free_swap_and_cache() only trylocks a
- * page, so it is just possible that the entry has been
- * truncated or holepunched since swap was confirmed.
- * shmem_undo_range() will have done some of the
- * unaccounting, now delete_from_swap_cache() will do
- * the rest.
- * Reset swap.val? No, leave it so "failed" goes back to
- * "repeat": reading a hole and writing should succeed.
- */
- if (error) {
- mem_cgroup_cancel_charge(page, memcg, false);
- delete_from_swap_cache(page);
- }
- }
- if (error)
- goto failed;
-
- mem_cgroup_commit_charge(page, memcg, true, false);
-
- spin_lock_irq(&info->lock);
- info->swapped--;
- shmem_recalc_inode(inode);
- spin_unlock_irq(&info->lock);
-
- if (sgp == SGP_WRITE)
- mark_page_accessed(page);
-
- delete_from_swap_cache(page);
- set_page_dirty(page);
- swap_free(swap);
-
- } else {
- if (vma && userfaultfd_missing(vma)) {
- *fault_type = handle_userfault(vmf, VM_UFFD_MISSING);
- return 0;
- }
+ if (vma && userfaultfd_missing(vma)) {
+ *fault_type = handle_userfault(vmf, VM_UFFD_MISSING);
+ return 0;
+ }

- /* shmem_symlink() */
- if (mapping->a_ops != &shmem_aops)
- goto alloc_nohuge;
- if (shmem_huge == SHMEM_HUGE_DENY || sgp_huge == SGP_NOHUGE)
- goto alloc_nohuge;
- if (shmem_huge == SHMEM_HUGE_FORCE)
+ /* shmem_symlink() */
+ if (mapping->a_ops != &shmem_aops)
+ goto alloc_nohuge;
+ if (shmem_huge == SHMEM_HUGE_DENY || sgp_huge == SGP_NOHUGE)
+ goto alloc_nohuge;
+ if (shmem_huge == SHMEM_HUGE_FORCE)
+ goto alloc_huge;
+ switch (sbinfo->huge) {
+ loff_t i_size;
+ pgoff_t off;
+ case SHMEM_HUGE_NEVER:
+ goto alloc_nohuge;
+ case SHMEM_HUGE_WITHIN_SIZE:
+ off = round_up(index, HPAGE_PMD_NR);
+ i_size = round_up(i_size_read(inode), PAGE_SIZE);
+ if (i_size >= HPAGE_PMD_SIZE &&
+ i_size >> PAGE_SHIFT >= off)
goto alloc_huge;
- switch (sbinfo->huge) {
- loff_t i_size;
- pgoff_t off;
- case SHMEM_HUGE_NEVER:
- goto alloc_nohuge;
- case SHMEM_HUGE_WITHIN_SIZE:
- off = round_up(index, HPAGE_PMD_NR);
- i_size = round_up(i_size_read(inode), PAGE_SIZE);
- if (i_size >= HPAGE_PMD_SIZE &&
- i_size >> PAGE_SHIFT >= off)
- goto alloc_huge;
- /* fallthrough */
- case SHMEM_HUGE_ADVISE:
- if (sgp_huge == SGP_HUGE)
- goto alloc_huge;
- /* TODO: implement fadvise() hints */
- goto alloc_nohuge;
- }
+ /* fallthrough */
+ case SHMEM_HUGE_ADVISE:
+ if (sgp_huge == SGP_HUGE)
+ goto alloc_huge;
+ /* TODO: implement fadvise() hints */
+ goto alloc_nohuge;
+ }

alloc_huge:
- page = shmem_alloc_and_acct_page(gfp, inode, index, true);
- if (IS_ERR(page)) {
-alloc_nohuge: page = shmem_alloc_and_acct_page(gfp, inode,
- index, false);
- }
- if (IS_ERR(page)) {
- int retry = 5;
- error = PTR_ERR(page);
- page = NULL;
- if (error != -ENOSPC)
- goto failed;
- /*
- * Try to reclaim some spece by splitting a huge page
- * beyond i_size on the filesystem.
- */
- while (retry--) {
- int ret;
- ret = shmem_unused_huge_shrink(sbinfo, NULL, 1);
- if (ret == SHRINK_STOP)
- break;
- if (ret)
- goto alloc_nohuge;
- }
- goto failed;
- }
-
- if (PageTransHuge(page))
- hindex = round_down(index, HPAGE_PMD_NR);
- else
- hindex = index;
+ page = shmem_alloc_and_acct_page(gfp, inode, index, true);
+ if (IS_ERR(page)) {
+alloc_nohuge:
+ page = shmem_alloc_and_acct_page(gfp, inode,
+ index, false);
+ }
+ if (IS_ERR(page)) {
+ int retry = 5;

- if (sgp == SGP_WRITE)
- __SetPageReferenced(page);
+ error = PTR_ERR(page);
+ page = NULL;
+ if (error != -ENOSPC)
+ goto unlock;
+ /*
+ * Try to reclaim some space by splitting a huge page
+ * beyond i_size on the filesystem.
+ */
+ while (retry--) {
+ int ret;

- error = mem_cgroup_try_charge_delay(page, charge_mm, gfp, &memcg,
- PageTransHuge(page));
- if (error)
- goto unacct;
- error = shmem_add_to_page_cache(page, mapping, hindex,
- NULL, gfp & GFP_RECLAIM_MASK);
- if (error) {
- mem_cgroup_cancel_charge(page, memcg,
- PageTransHuge(page));
- goto unacct;
+ ret = shmem_unused_huge_shrink(sbinfo, NULL, 1);
+ if (ret == SHRINK_STOP)
+ break;
+ if (ret)
+ goto alloc_nohuge;
}
- mem_cgroup_commit_charge(page, memcg, false,
- PageTransHuge(page));
- lru_cache_add_anon(page);
+ goto unlock;
+ }

- spin_lock_irq(&info->lock);
- info->alloced += 1 << compound_order(page);
- inode->i_blocks += BLOCKS_PER_PAGE << compound_order(page);
- shmem_recalc_inode(inode);
- spin_unlock_irq(&info->lock);
- alloced = true;
+ if (PageTransHuge(page))
+ hindex = round_down(index, HPAGE_PMD_NR);
+ else
+ hindex = index;

- if (PageTransHuge(page) &&
- DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE) <
- hindex + HPAGE_PMD_NR - 1) {
- /*
- * Part of the huge page is beyond i_size: subject
- * to shrink under memory pressure.
- */
- spin_lock(&sbinfo->shrinklist_lock);
- /*
- * _careful to defend against unlocked access to
- * ->shrink_list in shmem_unused_huge_shrink()
- */
- if (list_empty_careful(&info->shrinklist)) {
- list_add_tail(&info->shrinklist,
- &sbinfo->shrinklist);
- sbinfo->shrinklist_len++;
- }
- spin_unlock(&sbinfo->shrinklist_lock);
- }
+ if (sgp == SGP_WRITE)
+ __SetPageReferenced(page);
+
+ error = mem_cgroup_try_charge_delay(page, charge_mm, gfp, &memcg,
+ PageTransHuge(page));
+ if (error)
+ goto unacct;
+ error = shmem_add_to_page_cache(page, mapping, hindex,
+ NULL, gfp & GFP_RECLAIM_MASK);
+ if (error) {
+ mem_cgroup_cancel_charge(page, memcg,
+ PageTransHuge(page));
+ goto unacct;
+ }
+ mem_cgroup_commit_charge(page, memcg, false,
+ PageTransHuge(page));
+ lru_cache_add_anon(page);
+
+ spin_lock_irq(&info->lock);
+ info->alloced += 1 << compound_order(page);
+ inode->i_blocks += BLOCKS_PER_PAGE << compound_order(page);
+ shmem_recalc_inode(inode);
+ spin_unlock_irq(&info->lock);
+ alloced = true;

+ if (PageTransHuge(page) &&
+ DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE) <
+ hindex + HPAGE_PMD_NR - 1) {
/*
- * Let SGP_FALLOC use the SGP_WRITE optimization on a new page.
+ * Part of the huge page is beyond i_size: subject
+ * to shrink under memory pressure.
*/
- if (sgp == SGP_FALLOC)
- sgp = SGP_WRITE;
-clear:
+ spin_lock(&sbinfo->shrinklist_lock);
/*
- * Let SGP_WRITE caller clear ends if write does not fill page;
- * but SGP_FALLOC on a page fallocated earlier must initialize
- * it now, lest undo on failure cancel our earlier guarantee.
+ * _careful to defend against unlocked access to
+ * ->shrink_list in shmem_unused_huge_shrink()
*/
- if (sgp != SGP_WRITE && !PageUptodate(page)) {
- struct page *head = compound_head(page);
- int i;
+ if (list_empty_careful(&info->shrinklist)) {
+ list_add_tail(&info->shrinklist,
+ &sbinfo->shrinklist);
+ sbinfo->shrinklist_len++;
+ }
+ spin_unlock(&sbinfo->shrinklist_lock);
+ }

- for (i = 0; i < (1 << compound_order(head)); i++) {
- clear_highpage(head + i);
- flush_dcache_page(head + i);
- }
- SetPageUptodate(head);
+ /*
+ * Let SGP_FALLOC use the SGP_WRITE optimization on a new page.
+ */
+ if (sgp == SGP_FALLOC)
+ sgp = SGP_WRITE;
+clear:
+ /*
+ * Let SGP_WRITE caller clear ends if write does not fill page;
+ * but SGP_FALLOC on a page fallocated earlier must initialize
+ * it now, lest undo on failure cancel our earlier guarantee.
+ */
+ if (sgp != SGP_WRITE && !PageUptodate(page)) {
+ struct page *head = compound_head(page);
+ int i;
+
+ for (i = 0; i < (1 << compound_order(head)); i++) {
+ clear_highpage(head + i);
+ flush_dcache_page(head + i);
}
+ SetPageUptodate(head);
}

/* Perhaps the file has been truncated since we checked */
@@ -1879,9 +1921,6 @@ alloc_nohuge: page = shmem_alloc_and_acct_page(gfp, inode,
put_page(page);
goto alloc_nohuge;
}
-failed:
- if (swap.val && !shmem_confirm_swap(mapping, index, swap))
- error = -EEXIST;
unlock:
if (page) {
unlock_page(page);
--
2.17.1
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