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>
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2e0e26c76a
2 changed files with 45 additions and 35 deletions
57
mm/shmem.c
57
mm/shmem.c
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@ -838,10 +838,8 @@ static int shmem_unuse_inode(struct shmem_inode_info *info, swp_entry_t entry, s
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if (size > SHMEM_NR_DIRECT)
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size = SHMEM_NR_DIRECT;
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offset = shmem_find_swp(entry, ptr, ptr+size);
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if (offset >= 0) {
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shmem_swp_balance_unmap();
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if (offset >= 0)
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goto found;
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}
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if (!info->i_indirect)
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goto lost2;
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@ -879,11 +877,11 @@ static int shmem_unuse_inode(struct shmem_inode_info *info, swp_entry_t entry, s
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if (size > ENTRIES_PER_PAGE)
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size = ENTRIES_PER_PAGE;
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offset = shmem_find_swp(entry, ptr, ptr+size);
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shmem_swp_unmap(ptr);
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if (offset >= 0) {
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shmem_dir_unmap(dir);
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goto found;
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}
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shmem_swp_unmap(ptr);
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}
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}
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lost1:
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@ -893,10 +891,25 @@ static int shmem_unuse_inode(struct shmem_inode_info *info, swp_entry_t entry, s
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return 0;
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found:
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idx += offset;
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inode = &info->vfs_inode;
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error = add_to_page_cache(page, inode->i_mapping, idx, GFP_ATOMIC);
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inode = igrab(&info->vfs_inode);
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spin_unlock(&info->lock);
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/* move head to start search for next from here */
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list_move_tail(&shmem_swaplist, &info->swaplist);
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mutex_unlock(&shmem_swaplist_mutex);
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error = 1;
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if (!inode)
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goto out;
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spin_lock(&info->lock);
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ptr = shmem_swp_entry(info, idx, NULL);
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if (ptr && ptr->val == entry.val)
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error = add_to_page_cache(page, inode->i_mapping,
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idx, GFP_ATOMIC);
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if (error == -EEXIST) {
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struct page *filepage = find_get_page(inode->i_mapping, idx);
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error = 1;
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if (filepage) {
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/*
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* There might be a more uptodate page coming down
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@ -911,16 +924,18 @@ static int shmem_unuse_inode(struct shmem_inode_info *info, swp_entry_t entry, s
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delete_from_swap_cache(page);
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set_page_dirty(page);
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info->flags |= SHMEM_PAGEIN;
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shmem_swp_set(info, ptr + offset, 0);
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shmem_swp_set(info, ptr, 0);
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swap_free(entry);
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error = 1; /* not an error, but entry was found */
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}
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shmem_swp_unmap(ptr);
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if (ptr)
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shmem_swp_unmap(ptr);
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spin_unlock(&info->lock);
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/*
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* Decrement swap count even when the entry is left behind:
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* try_to_unuse will skip over mms, then reincrement count.
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*/
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swap_free(entry);
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return 1;
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out:
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unlock_page(page);
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page_cache_release(page);
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iput(inode); /* allows for NULL */
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return error;
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}
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/*
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@ -935,18 +950,16 @@ int shmem_unuse(swp_entry_t entry, struct page *page)
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mutex_lock(&shmem_swaplist_mutex);
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list_for_each_safe(p, next, &shmem_swaplist) {
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info = list_entry(p, struct shmem_inode_info, swaplist);
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if (!info->swapped)
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if (info->swapped)
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found = shmem_unuse_inode(info, entry, page);
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else
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list_del_init(&info->swaplist);
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else if (shmem_unuse_inode(info, entry, page)) {
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/* move head to start search for next from here */
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list_move_tail(&shmem_swaplist, &info->swaplist);
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found = 1;
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break;
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}
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cond_resched();
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if (found)
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goto out;
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}
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mutex_unlock(&shmem_swaplist_mutex);
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return found;
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out: return found; /* 0 or 1 or -ENOMEM */
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}
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/*
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@ -814,7 +814,7 @@ static int try_to_unuse(unsigned int type)
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atomic_inc(&new_start_mm->mm_users);
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atomic_inc(&prev_mm->mm_users);
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spin_lock(&mmlist_lock);
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while (*swap_map > 1 && !retval &&
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while (*swap_map > 1 && !retval && !shmem &&
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(p = p->next) != &start_mm->mmlist) {
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mm = list_entry(p, struct mm_struct, mmlist);
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if (!atomic_inc_not_zero(&mm->mm_users))
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@ -846,6 +846,13 @@ static int try_to_unuse(unsigned int type)
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mmput(start_mm);
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start_mm = new_start_mm;
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}
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if (shmem) {
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/* page has already been unlocked and released */
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if (shmem > 0)
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continue;
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retval = shmem;
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break;
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}
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if (retval) {
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unlock_page(page);
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page_cache_release(page);
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@ -884,12 +891,6 @@ static int try_to_unuse(unsigned int type)
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* read from disk into another page. Splitting into two
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* pages would be incorrect if swap supported "shared
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* private" pages, but they are handled by tmpfs files.
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*
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* Note shmem_unuse already deleted a swappage from
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* the swap cache, unless the move to filepage failed:
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* in which case it left swappage in cache, lowered its
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* swap count to pass quickly through the loops above,
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* and now we must reincrement count to try again later.
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*/
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if ((*swap_map > 1) && PageDirty(page) && PageSwapCache(page)) {
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struct writeback_control wbc = {
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@ -900,12 +901,8 @@ static int try_to_unuse(unsigned int type)
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lock_page(page);
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wait_on_page_writeback(page);
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}
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if (PageSwapCache(page)) {
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if (shmem)
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swap_duplicate(entry);
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else
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delete_from_swap_cache(page);
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}
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if (PageSwapCache(page))
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delete_from_swap_cache(page);
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/*
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* So we could skip searching mms once swap count went
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