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 <[email protected]>
---
mm/shmem.c | 57 +++++++++++++++++++++++++++++-------------------
mm/swapfile.c | 23 ++++++++-----------
2 files changed, 45 insertions(+), 35 deletions(-)
--- tmpfs6/mm/shmem.c 2007-12-06 16:34:56.000000000 +0000
+++ tmpfs7/mm/shmem.c 2007-12-06 18:11:26.000000000 +0000
@@ -838,10 +838,8 @@ static int shmem_unuse_inode(struct shme
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 shme
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, struc
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 */
}
/*
--- tmpfs6/mm/swapfile.c 2007-12-05 10:38:45.000000000 +0000
+++ tmpfs7/mm/swapfile.c 2007-12-06 17:00:18.000000000 +0000
@@ -823,7 +823,7 @@ static int try_to_unuse(unsigned int typ
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))
@@ -855,6 +855,13 @@ static int try_to_unuse(unsigned int typ
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);
@@ -893,12 +900,6 @@ static int try_to_unuse(unsigned int typ
* 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 = {
@@ -909,12 +910,8 @@ static int try_to_unuse(unsigned int typ
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
--
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