Hugh Dickins wrote:
<cut>
Here's the patch I was testing last night, but I do want to test it
some more (I've not even tried your unmounting case yet), and I do want
to make some changes to it (some comments, and see if I can move the
mem_cgroup_cache_charge outside of the mutex, making it GFP_KERNEL
rather than GFP_NOFS - at the time that mem_cgroup charging went in,
we did not know here if it was actually a shmem swap page, whereas
nowadays we can be sure, since that's noted in the swap_map).
In shmem_unuse_inode I'm widening the shmem_swaplist_mutex to protect
against shmem_evict_inode; and in shmem_writepage adding to the list
earlier, while holding lock on page still in pagecache to protect it.
But testing last night showed corruption on this laptop (no problem
on other machines): I'm guessing it's unrelated, but I can't be sure
of that without more extended testing.
Hugh
This patch fixed my problem, I didn't catch any crashes on my test-case: swapout-unmount.
--- 2.6.39-rc5/mm/shmem.c 2011-04-28 09:52:49.066135001 -0700
+++ linux/mm/shmem.c 2011-05-02 21:02:21.745633214 -0700
@@ -852,7 +852,7 @@ static inline int shmem_find_swp(swp_ent
static int shmem_unuse_inode(struct shmem_inode_info *info, swp_entry_t entry, struct page *page)
{
- struct inode *inode;
+ struct address_space *mapping;
unsigned long idx;
unsigned long size;
unsigned long limit;
@@ -928,7 +928,7 @@ lost2:
return 0;
found:
idx += offset;
- inode = igrab(&info->vfs_inode);
+ mapping = info->vfs_inode.i_mapping;
spin_unlock(&info->lock);
/*
@@ -940,20 +940,16 @@ found:
*/
if (shmem_swaplist.next !=&info->swaplist)
list_move_tail(&shmem_swaplist,&info->swaplist);
- mutex_unlock(&shmem_swaplist_mutex);
- error = 1;
- if (!inode)
- goto out;
/*
- * Charge page using GFP_KERNEL while we can wait.
+ * Charge page using GFP_NOFS while we can wait.
* Charged back to the user(not to caller) when swap account is used.
* add_to_page_cache() will be called with GFP_NOWAIT.
*/
- error = mem_cgroup_cache_charge(page, current->mm, GFP_KERNEL);
+ error = mem_cgroup_cache_charge(page, current->mm, GFP_NOFS);
if (error)
goto out;
- error = radix_tree_preload(GFP_KERNEL);
+ error = radix_tree_preload(GFP_NOFS);
if (error) {
mem_cgroup_uncharge_cache_page(page);
goto out;
@@ -963,14 +959,14 @@ found:
spin_lock(&info->lock);
ptr = shmem_swp_entry(info, idx, NULL);
if (ptr&& ptr->val == entry.val) {
- error = add_to_page_cache_locked(page, inode->i_mapping,
+ error = add_to_page_cache_locked(page, mapping,
idx, GFP_NOWAIT);
/* does mem_cgroup_uncharge_cache_page on error */
} else /* we must compensate for our precharge above */
mem_cgroup_uncharge_cache_page(page);
if (error == -EEXIST) {
- struct page *filepage = find_get_page(inode->i_mapping, idx);
+ struct page *filepage = find_get_page(mapping, idx);
error = 1;
if (filepage) {
/*
@@ -995,9 +991,6 @@ found:
spin_unlock(&info->lock);
radix_tree_preload_end();
out:
- unlock_page(page);
- page_cache_release(page);
- iput(inode); /* allows for NULL */
return error;
}
@@ -1016,7 +1009,7 @@ int shmem_unuse(swp_entry_t entry, struc
found = shmem_unuse_inode(info, entry, page);
cond_resched();
if (found)
- goto out;
+ break;
}
mutex_unlock(&shmem_swaplist_mutex);
/*
@@ -1025,7 +1018,6 @@ int shmem_unuse(swp_entry_t entry, struc
*/
unlock_page(page);
page_cache_release(page);
-out:
return (found< 0) ? found : 0;
}
@@ -1039,6 +1031,7 @@ static int shmem_writepage(struct page *
struct address_space *mapping;
unsigned long index;
struct inode *inode;
+ bool unlock_mutex = false;
BUG_ON(!PageLocked(page));
mapping = page->mapping;
@@ -1064,7 +1057,17 @@ static int shmem_writepage(struct page *
else
swap.val = 0;
+ if (swap.val&& list_empty(&info->swaplist)) {
+ mutex_lock(&shmem_swaplist_mutex);
+ /* move instead of add in case we're racing */
+ list_move_tail(&info->swaplist,&shmem_swaplist);
+ unlock_mutex = true;
+ }
+
spin_lock(&info->lock);
+ if (unlock_mutex)
+ mutex_unlock(&shmem_swaplist_mutex);
+
if (index>= info->next_index) {
BUG_ON(!(info->flags& SHMEM_TRUNCATE));
goto unlock;
@@ -1084,21 +1087,10 @@ static int shmem_writepage(struct page *
delete_from_page_cache(page);
shmem_swp_set(info, entry, swap.val);
shmem_swp_unmap(entry);
- if (list_empty(&info->swaplist))
- inode = igrab(inode);
- else
- inode = NULL;
spin_unlock(&info->lock);
swap_shmem_alloc(swap);
BUG_ON(page_mapped(page));
swap_writepage(page, wbc);
- if (inode) {
- mutex_lock(&shmem_swaplist_mutex);
- /* move instead of add in case we're racing */
- list_move_tail(&info->swaplist,&shmem_swaplist);
- mutex_unlock(&shmem_swaplist_mutex);
- iput(inode);
- }
return 0;
}
--
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