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tmpfs: open a window in shmem_unuse_inode 

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>
This commit is contained in:
Hugh Dickins 2008-02-04 22:28:53 -08:00 committed by Linus Torvalds
parent cb5f7b9a47
commit 2e0e26c76a
2 changed files with 45 additions and 35 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

57
mm/shmem.c
View 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 @@ static int shmem_unuse_inode(struct shmem_inode_info *info, swp_entry_t entry, s
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 @@ static int shmem_unuse_inode(struct shmem_inode_info *info, swp_entry_t entry, s
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 */
}
/*

23
mm/swapfile.c
View 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