shmem_unuse_inode() and shmem_writepage() contain a little code to
cope with pages inserted independently into the filecache, probably
by a filesystem stacked on top of tmpfs, then fed to its ->readpage()
or ->writepage().
Unionfs was indeed experimenting with working in that way three years
ago, but I find no current examples: nowadays the stacking filesystems
use vfs interfaces to the lower filesystem.
It's now illegal: remove most of that code, adding some WARN_ON_ONCEs.
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Erez Zadok <ezk@xxxxxxxxxxxxxxxxx>
---
mm/shmem.c | 50 ++++++++++++++++----------------------------------
1 file changed, 16 insertions(+), 34 deletions(-)
--- linux.orig/mm/shmem.c 2011-06-09 11:39:50.369329884 -0700
+++ linux/mm/shmem.c 2011-06-09 11:40:02.761391246 -0700
@@ -972,20 +972,7 @@ found:
error = add_to_page_cache_locked(page, mapping, idx, GFP_NOWAIT);
/* which does mem_cgroup_uncharge_cache_page on error */
- if (error == -EEXIST) {
- struct page *filepage = find_get_page(mapping, idx);
- error = 1;
- if (filepage) {
- /*
- * There might be a more uptodate page coming down
- * from a stacked writepage: forget our swappage if so.
- */
- if (PageUptodate(filepage))
- error = 0;
- page_cache_release(filepage);
- }
- }
- if (!error) {
+ if (error != -ENOMEM) {
delete_from_swap_cache(page);
set_page_dirty(page);
info->flags |= SHMEM_PAGEIN;
@@ -1072,16 +1059,17 @@ static int shmem_writepage(struct page *
/*
* shmem_backing_dev_info's capabilities prevent regular writeback or
* sync from ever calling shmem_writepage; but a stacking filesystem
- * may use the ->writepage of its underlying filesystem, in which case
+ * might use ->writepage of its underlying filesystem, in which case
* tmpfs should write out to swap only in response to memory pressure,
- * and not for the writeback threads or sync. However, in those cases,
- * we do still want to check if there's a redundant swappage to be
- * discarded.
+ * and not for the writeback threads or sync.
*/
- if (wbc->for_reclaim)
- swap = get_swap_page();
- else
- swap.val = 0;
+ if (!wbc->for_reclaim) {
+ WARN_ON_ONCE(1); /* Still happens? Tell us about it! */
+ goto redirty;
+ }
+ swap = get_swap_page();
+ if (!swap.val)
+ goto redirty;
/*
* Add inode to shmem_unuse()'s list of swapped-out inodes,
@@ -1092,15 +1080,12 @@ static int shmem_writepage(struct page *
* we've taken the spinlock, because shmem_unuse_inode() will
* prune a !swapped inode from the swaplist under both locks.
*/
- if (swap.val) {
- mutex_lock(&shmem_swaplist_mutex);
- if (list_empty(&info->swaplist))
- list_add_tail(&info->swaplist, &shmem_swaplist);
- }
+ mutex_lock(&shmem_swaplist_mutex);
+ if (list_empty(&info->swaplist))
+ list_add_tail(&info->swaplist, &shmem_swaplist);
spin_lock(&info->lock);
- if (swap.val)
- mutex_unlock(&shmem_swaplist_mutex);
+ mutex_unlock(&shmem_swaplist_mutex);
if (index >= info->next_index) {
BUG_ON(!(info->flags & SHMEM_TRUNCATE));
@@ -1108,16 +1093,13 @@ static int shmem_writepage(struct page *
}
entry = shmem_swp_entry(info, index, NULL);
if (entry->val) {
- /*
- * The more uptodate page coming down from a stacked
- * writepage should replace our old swappage.
- */
+ WARN_ON_ONCE(1); /* Still happens? Tell us about it! */
free_swap_and_cache(*entry);
shmem_swp_set(info, entry, 0);
}
shmem_recalc_inode(inode);
- if (swap.val && add_to_swap_cache(page, swap, GFP_ATOMIC) == 0) {
+ if (add_to_swap_cache(page, swap, GFP_ATOMIC) == 0) {
delete_from_page_cache(page);
shmem_swp_set(info, entry, swap.val);
shmem_swp_unmap(entry);
--
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