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Commit 2e0e26c7 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
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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: default avatarHugh Dickins <hugh@veritas.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent cb5f7b9a

mm/shmem.c

+35 −22
Original line number Diff line number Diff line
@@ -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 @@ 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 */

	}

	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 */

}



/*

mm/swapfile.c

+10 −13
Original line number Diff line number Diff line
@@ -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

		if (PageSwapCache(page))

			delete_from_swap_cache(page);

		}



		/*

		 * So we could skip searching mms once swap count went