Move out the code for unusing swap entries from loop in try_to_unuse()
to separate function: try_to_unuse_swp_entry(). Export this new function
in swapfile.h just like try_to_unuse() is exported.
This new function will be used for unusing swap entries from subsystems
(e.g. zswap).
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@xxxxxxxxxxx>
---
include/linux/swapfile.h | 2 +
mm/swapfile.c | 356 ++++++++++++++++++++++++----------------------
2 files changed, 189 insertions(+), 169 deletions(-)
diff --git a/include/linux/swapfile.h b/include/linux/swapfile.h
index e282624..68c24a7 100644
--- a/include/linux/swapfile.h
+++ b/include/linux/swapfile.h
@@ -9,5 +9,7 @@ extern spinlock_t swap_lock;
extern struct swap_list_t swap_list;
extern struct swap_info_struct *swap_info[];
extern int try_to_unuse(unsigned int, bool, unsigned long);
+extern int try_to_unuse_swp_entry(struct mm_struct **start_mm,
+ struct swap_info_struct *si, swp_entry_t entry);
#endif /* _LINUX_SWAPFILE_H */
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 36af6ee..4ba21ec 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1100,6 +1100,190 @@ static unsigned int find_next_to_unuse(struct swap_info_struct *si,
}
/*
+ * Returns:
+ * - negative on error,
+ * - 0 on success (entry unused, freed independently or shmem entry
+ * already released)
+ */
+int try_to_unuse_swp_entry(struct mm_struct **start_mm,
+ struct swap_info_struct *si, swp_entry_t entry)
+{
+ pgoff_t offset = swp_offset(entry);
+ unsigned char *swap_map;
+ unsigned char swcount;
+ struct page *page;
+ int retval = 0;
+
+ if (signal_pending(current)) {
+ retval = -EINTR;
+ goto out;
+ }
+
+ /*
+ * Get a page for the entry, using the existing swap
+ * cache page if there is one. Otherwise, get a clean
+ * page and read the swap into it.
+ */
+ swap_map = &si->swap_map[offset];
+ page = read_swap_cache_async(entry,
+ GFP_HIGHUSER_MOVABLE, NULL, 0);
+ if (!page) {
+ /*
+ * Either swap_duplicate() failed because entry
+ * has been freed independently, and will not be
+ * reused since sys_swapoff() already disabled
+ * allocation from here, or alloc_page() failed.
+ */
+ if (!*swap_map)
+ retval = 0;
+ else
+ retval = -ENOMEM;
+ goto out;
+ }
+
+ /*
+ * Don't hold on to start_mm if it looks like exiting.
+ */
+ if (atomic_read(&(*start_mm)->mm_users) == 1) {
+ mmput(*start_mm);
+ *start_mm = &init_mm;
+ atomic_inc(&init_mm.mm_users);
+ }
+
+ /*
+ * Wait for and lock page. When do_swap_page races with
+ * try_to_unuse, do_swap_page can handle the fault much
+ * faster than try_to_unuse can locate the entry. This
+ * apparently redundant "wait_on_page_locked" lets try_to_unuse
+ * defer to do_swap_page in such a case - in some tests,
+ * do_swap_page and try_to_unuse repeatedly compete.
+ */
+ wait_on_page_locked(page);
+ wait_on_page_writeback(page);
+ lock_page(page);
+ wait_on_page_writeback(page);
+
+ /*
+ * Remove all references to entry.
+ */
+ swcount = *swap_map;
+ if (swap_count(swcount) == SWAP_MAP_SHMEM) {
+ retval = shmem_unuse(entry, page);
+ VM_BUG_ON(retval > 0);
+ /* page has already been unlocked and released */
+ goto out;
+ }
+ if (swap_count(swcount) && *start_mm != &init_mm)
+ retval = unuse_mm(*start_mm, entry, page);
+
+ if (swap_count(*swap_map)) {
+ int set_start_mm = (*swap_map >= swcount);
+ struct list_head *p = &(*start_mm)->mmlist;
+ struct mm_struct *new_start_mm = *start_mm;
+ struct mm_struct *prev_mm = *start_mm;
+ struct mm_struct *mm;
+
+ atomic_inc(&new_start_mm->mm_users);
+ atomic_inc(&prev_mm->mm_users);
+ spin_lock(&mmlist_lock);
+ while (swap_count(*swap_map) && !retval &&
+ (p = p->next) != &(*start_mm)->mmlist) {
+ mm = list_entry(p, struct mm_struct, mmlist);
+ if (!atomic_inc_not_zero(&mm->mm_users))
+ continue;
+ spin_unlock(&mmlist_lock);
+ mmput(prev_mm);
+ prev_mm = mm;
+
+ cond_resched();
+
+ swcount = *swap_map;
+ if (!swap_count(swcount)) /* any usage ? */
+ ;
+ else if (mm == &init_mm)
+ set_start_mm = 1;
+ else
+ retval = unuse_mm(mm, entry, page);
+
+ if (set_start_mm && *swap_map < swcount) {
+ mmput(new_start_mm);
+ atomic_inc(&mm->mm_users);
+ new_start_mm = mm;
+ set_start_mm = 0;
+ }
+ spin_lock(&mmlist_lock);
+ }
+ spin_unlock(&mmlist_lock);
+ mmput(prev_mm);
+ mmput(*start_mm);
+ *start_mm = new_start_mm;
+ }
+ if (retval) {
+ unlock_page(page);
+ page_cache_release(page);
+ goto out;
+ }
+
+ /*
+ * If a reference remains (rare), we would like to leave
+ * the page in the swap cache; but try_to_unmap could
+ * then re-duplicate the entry once we drop page lock,
+ * so we might loop indefinitely; also, that page could
+ * not be swapped out to other storage meanwhile. So:
+ * delete from cache even if there's another reference,
+ * after ensuring that the data has been saved to disk -
+ * since if the reference remains (rarer), it will be
+ * read from disk into another page. Splitting into two
+ * pages would be incorrect if swap supported "shared
+ * private" pages, but they are handled by tmpfs files.
+ *
+ * Given how unuse_vma() targets one particular offset
+ * in an anon_vma, once the anon_vma has been determined,
+ * this splitting happens to be just what is needed to
+ * handle where KSM pages have been swapped out: re-reading
+ * is unnecessarily slow, but we can fix that later on.
+ */
+ if (swap_count(*swap_map) &&
+ PageDirty(page) && PageSwapCache(page)) {
+ struct writeback_control wbc = {
+ .sync_mode = WB_SYNC_NONE,
+ };
+
+ swap_writepage(page, &wbc);
+ lock_page(page);
+ wait_on_page_writeback(page);
+ }
+
+ /*
+ * It is conceivable that a racing task removed this page from
+ * swap cache just before we acquired the page lock at the top,
+ * or while we dropped it in unuse_mm(). The page might even
+ * be back in swap cache on another swap area: that we must not
+ * delete, since it may not have been written out to swap yet.
+ */
+ if (PageSwapCache(page) &&
+ likely(page_private(page) == entry.val))
+ delete_from_swap_cache(page);
+
+ /*
+ * So we could skip searching mms once swap count went
+ * to 1, we did not mark any present ptes as dirty: must
+ * mark page dirty so shrink_page_list will preserve it.
+ */
+ SetPageDirty(page);
+ unlock_page(page);
+ page_cache_release(page);
+
+ /*
+ * Make sure that we aren't completely killing
+ * interactive performance.
+ */
+ cond_resched();
+out:
+ return retval;
+}
+
+/*
* We completely avoid races by reading each swap page in advance,
* and then search for the process using it. All the necessary
* page table adjustments can then be made atomically.
@@ -1112,10 +1296,6 @@ int try_to_unuse(unsigned int type, bool frontswap,
{
struct swap_info_struct *si = swap_info[type];
struct mm_struct *start_mm;
- unsigned char *swap_map;
- unsigned char swcount;
- struct page *page;
- swp_entry_t entry;
unsigned int i = 0;
int retval = 0;
@@ -1142,172 +1322,10 @@ 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) {
- if (signal_pending(current)) {
- retval = -EINTR;
- break;
- }
-
- /*
- * Get a page for the entry, using the existing swap
- * cache page if there is one. Otherwise, get a clean
- * page and read the swap into it.
- */
- swap_map = &si->swap_map[i];
- entry = swp_entry(type, i);
- page = read_swap_cache_async(entry,
- GFP_HIGHUSER_MOVABLE, NULL, 0);
- if (!page) {
- /*
- * Either swap_duplicate() failed because entry
- * has been freed independently, and will not be
- * reused since sys_swapoff() already disabled
- * allocation from here, or alloc_page() failed.
- */
- if (!*swap_map)
- continue;
- retval = -ENOMEM;
- break;
- }
-
- /*
- * Don't hold on to start_mm if it looks like exiting.
- */
- if (atomic_read(&start_mm->mm_users) == 1) {
- mmput(start_mm);
- start_mm = &init_mm;
- atomic_inc(&init_mm.mm_users);
- }
-
- /*
- * Wait for and lock page. When do_swap_page races with
- * try_to_unuse, do_swap_page can handle the fault much
- * faster than try_to_unuse can locate the entry. This
- * apparently redundant "wait_on_page_locked" lets try_to_unuse
- * defer to do_swap_page in such a case - in some tests,
- * do_swap_page and try_to_unuse repeatedly compete.
- */
- wait_on_page_locked(page);
- wait_on_page_writeback(page);
- lock_page(page);
- wait_on_page_writeback(page);
-
- /*
- * Remove all references to entry.
- */
- swcount = *swap_map;
- if (swap_count(swcount) == SWAP_MAP_SHMEM) {
- retval = shmem_unuse(entry, page);
- /* page has already been unlocked and released */
- if (retval < 0)
- break;
- continue;
- }
- if (swap_count(swcount) && start_mm != &init_mm)
- retval = unuse_mm(start_mm, entry, page);
-
- if (swap_count(*swap_map)) {
- int set_start_mm = (*swap_map >= swcount);
- struct list_head *p = &start_mm->mmlist;
- struct mm_struct *new_start_mm = start_mm;
- struct mm_struct *prev_mm = start_mm;
- struct mm_struct *mm;
-
- atomic_inc(&new_start_mm->mm_users);
- atomic_inc(&prev_mm->mm_users);
- spin_lock(&mmlist_lock);
- while (swap_count(*swap_map) && !retval &&
- (p = p->next) != &start_mm->mmlist) {
- mm = list_entry(p, struct mm_struct, mmlist);
- if (!atomic_inc_not_zero(&mm->mm_users))
- continue;
- spin_unlock(&mmlist_lock);
- mmput(prev_mm);
- prev_mm = mm;
-
- cond_resched();
-
- swcount = *swap_map;
- if (!swap_count(swcount)) /* any usage ? */
- ;
- else if (mm == &init_mm)
- set_start_mm = 1;
- else
- retval = unuse_mm(mm, entry, page);
-
- if (set_start_mm && *swap_map < swcount) {
- mmput(new_start_mm);
- atomic_inc(&mm->mm_users);
- new_start_mm = mm;
- set_start_mm = 0;
- }
- spin_lock(&mmlist_lock);
- }
- spin_unlock(&mmlist_lock);
- mmput(prev_mm);
- mmput(start_mm);
- start_mm = new_start_mm;
- }
- if (retval) {
- unlock_page(page);
- page_cache_release(page);
+ retval = try_to_unuse_swp_entry(&start_mm, si,
+ swp_entry(type, i));
+ if (retval != 0)
break;
- }
-
- /*
- * If a reference remains (rare), we would like to leave
- * the page in the swap cache; but try_to_unmap could
- * then re-duplicate the entry once we drop page lock,
- * so we might loop indefinitely; also, that page could
- * not be swapped out to other storage meanwhile. So:
- * delete from cache even if there's another reference,
- * after ensuring that the data has been saved to disk -
- * since if the reference remains (rarer), it will be
- * read from disk into another page. Splitting into two
- * pages would be incorrect if swap supported "shared
- * private" pages, but they are handled by tmpfs files.
- *
- * Given how unuse_vma() targets one particular offset
- * in an anon_vma, once the anon_vma has been determined,
- * this splitting happens to be just what is needed to
- * handle where KSM pages have been swapped out: re-reading
- * is unnecessarily slow, but we can fix that later on.
- */
- if (swap_count(*swap_map) &&
- PageDirty(page) && PageSwapCache(page)) {
- struct writeback_control wbc = {
- .sync_mode = WB_SYNC_NONE,
- };
-
- swap_writepage(page, &wbc);
- lock_page(page);
- wait_on_page_writeback(page);
- }
-
- /*
- * It is conceivable that a racing task removed this page from
- * swap cache just before we acquired the page lock at the top,
- * or while we dropped it in unuse_mm(). The page might even
- * be back in swap cache on another swap area: that we must not
- * delete, since it may not have been written out to swap yet.
- */
- if (PageSwapCache(page) &&
- likely(page_private(page) == entry.val))
- delete_from_swap_cache(page);
-
- /*
- * So we could skip searching mms once swap count went
- * to 1, we did not mark any present ptes as dirty: must
- * mark page dirty so shrink_page_list will preserve it.
- */
- SetPageDirty(page);
- unlock_page(page);
- page_cache_release(page);
-
- /*
- * Make sure that we aren't completely killing
- * interactive performance.
- */
- cond_resched();
if (frontswap && pages_to_unuse > 0) {
if (!--pages_to_unuse)
break;
--
1.7.9.5
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