tmpfs: open a window in shmem_unuse_inode
Hugh Dickins [Tue, 5 Feb 2008 06:28:53 +0000 (22:28 -0800)]
There are a couple of reasons (patches follow) why it would be good to open a
window for sleep in shmem_unuse_inode, between its search for a matching swap
entry, and its handling of the entry found.

shmem_unuse_inode must then use igrab to hold the inode against deletion in
that window, and its corresponding iput might result in deletion: so it had
better unlock_page before the iput, and might as well release the page too.

Nor is there any need to hold on to shmem_swaplist_mutex once we know we'll
leave the loop.  So this unwinding moves from try_to_unuse and shmem_unuse
into shmem_unuse_inode, in the case when it finds a match.

Let try_to_unuse break on error in the shmem_unuse case, as it does in the
unuse_mm case: though at this point in the series, no error to break on.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/shmem.c
mm/swapfile.c

index 2e03d60..a0126c4 100644 (file)
@@ -838,10 +838,8 @@ static int shmem_unuse_inode(struct shmem_inode_info *info, swp_entry_t entry, s
        if (size > SHMEM_NR_DIRECT)
                size = SHMEM_NR_DIRECT;
        offset = shmem_find_swp(entry, ptr, ptr+size);
-       if (offset >= 0) {
-               shmem_swp_balance_unmap();
+       if (offset >= 0)
                goto found;
-       }
        if (!info->i_indirect)
                goto lost2;
 
@@ -879,11 +877,11 @@ static int shmem_unuse_inode(struct shmem_inode_info *info, swp_entry_t entry, s
                        if (size > ENTRIES_PER_PAGE)
                                size = ENTRIES_PER_PAGE;
                        offset = shmem_find_swp(entry, ptr, ptr+size);
+                       shmem_swp_unmap(ptr);
                        if (offset >= 0) {
                                shmem_dir_unmap(dir);
                                goto found;
                        }
-                       shmem_swp_unmap(ptr);
                }
        }
 lost1:
@@ -893,10 +891,25 @@ lost2:
        return 0;
 found:
        idx += offset;
-       inode = &info->vfs_inode;
-       error = add_to_page_cache(page, inode->i_mapping, idx, GFP_ATOMIC);
+       inode = igrab(&info->vfs_inode);
+       spin_unlock(&info->lock);
+
+       /* move head to start search for next from here */
+       list_move_tail(&shmem_swaplist, &info->swaplist);
+       mutex_unlock(&shmem_swaplist_mutex);
+
+       error = 1;
+       if (!inode)
+               goto out;
+
+       spin_lock(&info->lock);
+       ptr = shmem_swp_entry(info, idx, NULL);
+       if (ptr && ptr->val == entry.val)
+               error = add_to_page_cache(page, inode->i_mapping,
+                                               idx, GFP_ATOMIC);
        if (error == -EEXIST) {
                struct page *filepage = find_get_page(inode->i_mapping, idx);
+               error = 1;
                if (filepage) {
                        /*
                         * There might be a more uptodate page coming down
@@ -911,16 +924,18 @@ found:
                delete_from_swap_cache(page);
                set_page_dirty(page);
                info->flags |= SHMEM_PAGEIN;
-               shmem_swp_set(info, ptr + offset, 0);
+               shmem_swp_set(info, ptr, 0);
+               swap_free(entry);
+               error = 1;      /* not an error, but entry was found */
        }
-       shmem_swp_unmap(ptr);
+       if (ptr)
+               shmem_swp_unmap(ptr);
        spin_unlock(&info->lock);
-       /*
-        * Decrement swap count even when the entry is left behind:
-        * try_to_unuse will skip over mms, then reincrement count.
-        */
-       swap_free(entry);
-       return 1;
+out:
+       unlock_page(page);
+       page_cache_release(page);
+       iput(inode);            /* allows for NULL */
+       return error;
 }
 
 /*
@@ -935,18 +950,16 @@ int shmem_unuse(swp_entry_t entry, struct page *page)
        mutex_lock(&shmem_swaplist_mutex);
        list_for_each_safe(p, next, &shmem_swaplist) {
                info = list_entry(p, struct shmem_inode_info, swaplist);
-               if (!info->swapped)
+               if (info->swapped)
+                       found = shmem_unuse_inode(info, entry, page);
+               else
                        list_del_init(&info->swaplist);
-               else if (shmem_unuse_inode(info, entry, page)) {
-                       /* move head to start search for next from here */
-                       list_move_tail(&shmem_swaplist, &info->swaplist);
-                       found = 1;
-                       break;
-               }
                cond_resched();
+               if (found)
+                       goto out;
        }
        mutex_unlock(&shmem_swaplist_mutex);
-       return found;
+out:   return found;   /* 0 or 1 or -ENOMEM */
 }
 
 /*
index 14bc4f2..eade24d 100644 (file)
@@ -814,7 +814,7 @@ static int try_to_unuse(unsigned int type)
                        atomic_inc(&new_start_mm->mm_users);
                        atomic_inc(&prev_mm->mm_users);
                        spin_lock(&mmlist_lock);
-                       while (*swap_map > 1 && !retval &&
+                       while (*swap_map > 1 && !retval && !shmem &&
                                        (p = p->next) != &start_mm->mmlist) {
                                mm = list_entry(p, struct mm_struct, mmlist);
                                if (!atomic_inc_not_zero(&mm->mm_users))
@@ -846,6 +846,13 @@ static int try_to_unuse(unsigned int type)
                        mmput(start_mm);
                        start_mm = new_start_mm;
                }
+               if (shmem) {
+                       /* page has already been unlocked and released */
+                       if (shmem > 0)
+                               continue;
+                       retval = shmem;
+                       break;
+               }
                if (retval) {
                        unlock_page(page);
                        page_cache_release(page);
@@ -884,12 +891,6 @@ static int try_to_unuse(unsigned int type)
                 * 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.
-                *
-                * Note shmem_unuse already deleted a swappage from
-                * the swap cache, unless the move to filepage failed:
-                * in which case it left swappage in cache, lowered its
-                * swap count to pass quickly through the loops above,
-                * and now we must reincrement count to try again later.
                 */
                if ((*swap_map > 1) && PageDirty(page) && PageSwapCache(page)) {
                        struct writeback_control wbc = {
@@ -900,12 +901,8 @@ static int try_to_unuse(unsigned int type)
                        lock_page(page);
                        wait_on_page_writeback(page);
                }
-               if (PageSwapCache(page)) {
-                       if (shmem)
-                               swap_duplicate(entry);
-                       else
-                               delete_from_swap_cache(page);
-               }
+               if (PageSwapCache(page))
+                       delete_from_swap_cache(page);
 
                /*
                 * So we could skip searching mms once swap count went