Commit 8a57d9d6 authored by Curt Wohlgemuth's avatar Curt Wohlgemuth Committed by Theodore Ts'o
Browse files

ext4: check for a good block group before loading buddy pages 



This adds a new field in ext4_group_info to cache the largest available
block range in a block group; and don't load the buddy pages until *after*
we've done a sanity check on the block group.

With large allocation requests (e.g., fallocate(), 8MiB) and relatively full
partitions, it's easy to have no block groups with a block extent large
enough to satisfy the input request length.  This currently causes the loop
during cr == 0 in ext4_mb_regular_allocator() to load the buddy bitmap pages
for EVERY block group.  That can be a lot of pages.  The patch below allows
us to call ext4_mb_good_group() BEFORE we load the buddy pages (although we
have check again after we lock the block group).

Addresses-Google-Bug: #2578108
Addresses-Google-Bug: #2704453

Signed-off-by: default avatarCurt Wohlgemuth <curtw@google.com>
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent 6d19c42b

fs/ext4/ext4.h

+1 −0
Original line number Diff line number Diff line
@@ -1678,6 +1678,7 @@ struct ext4_group_info { 
	ext4_grpblk_t	bb_first_free;	/* first free block */

	ext4_grpblk_t	bb_free;	/* total free blocks */

	ext4_grpblk_t	bb_fragments;	/* nr of freespace fragments */

	ext4_grpblk_t	bb_largest_free_order;/* order of largest frag in BG */

	struct          list_head bb_prealloc_list;

#ifdef DOUBLE_CHECK

	void            *bb_bitmap;

fs/ext4/mballoc.c

+57 −13
Original line number Diff line number Diff line
@@ -658,6 +658,27 @@ static void ext4_mb_mark_free_simple(struct super_block *sb, 
	}

}



/*

 * Cache the order of the largest free extent we have available in this block

 * group.

 */

static void

mb_set_largest_free_order(struct super_block *sb, struct ext4_group_info *grp)

{

	int i;

	int bits;



	grp->bb_largest_free_order = -1; /* uninit */



	bits = sb->s_blocksize_bits + 1;

	for (i = bits; i >= 0; i--) {

		if (grp->bb_counters[i] > 0) {

			grp->bb_largest_free_order = i;

			break;

		}

	}

}



static noinline_for_stack

void ext4_mb_generate_buddy(struct super_block *sb,

				void *buddy, void *bitmap, ext4_group_t group)
@@ -700,6 +721,7 @@ void ext4_mb_generate_buddy(struct super_block *sb, 
		 */

		grp->bb_free = free;

	}

	mb_set_largest_free_order(sb, grp);



	clear_bit(EXT4_GROUP_INFO_NEED_INIT_BIT, &(grp->bb_state));
@@ -725,6 +747,9 @@ void ext4_mb_generate_buddy(struct super_block *sb, 
 * contain blocks_per_page (PAGE_CACHE_SIZE / blocksize)  blocks.

 * So it can have information regarding groups_per_page which

 * is blocks_per_page/2

 *

 * Locking note:  This routine takes the block group lock of all groups

 * for this page; do not hold this lock when calling this routine!

 */



static int ext4_mb_init_cache(struct page *page, char *incore)
@@ -910,6 +935,11 @@ out: 
	return err;

}



/*

 * Locking note:  This routine calls ext4_mb_init_cache(), which takes the

 * block group lock of all groups for this page; do not hold the BG lock when

 * calling this routine!

 */

static noinline_for_stack

int ext4_mb_init_group(struct super_block *sb, ext4_group_t group)

{
@@ -1004,6 +1034,11 @@ err: 
	return ret;

}



/*

 * Locking note:  This routine calls ext4_mb_init_cache(), which takes the

 * block group lock of all groups for this page; do not hold the BG lock when

 * calling this routine!

 */

static noinline_for_stack int

ext4_mb_load_buddy(struct super_block *sb, ext4_group_t group,

					struct ext4_buddy *e4b)
@@ -1299,6 +1334,7 @@ static void mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b, 
			buddy = buddy2;

		} while (1);

	}

	mb_set_largest_free_order(sb, e4b->bd_info);

	mb_check_buddy(e4b);

}
@@ -1427,6 +1463,7 @@ static int mb_mark_used(struct ext4_buddy *e4b, struct ext4_free_extent *ex) 
		e4b->bd_info->bb_counters[ord]++;

		e4b->bd_info->bb_counters[ord]++;

	}

	mb_set_largest_free_order(e4b->bd_sb, e4b->bd_info);



	mb_set_bits(EXT4_MB_BITMAP(e4b), ex->fe_start, len0);

	mb_check_buddy(e4b);
@@ -1821,16 +1858,22 @@ void ext4_mb_scan_aligned(struct ext4_allocation_context *ac, 
	}

}



/* This is now called BEFORE we load the buddy bitmap. */

static int ext4_mb_good_group(struct ext4_allocation_context *ac,

				ext4_group_t group, int cr)

{

	unsigned free, fragments;

	unsigned i, bits;

	int flex_size = ext4_flex_bg_size(EXT4_SB(ac->ac_sb));

	struct ext4_group_info *grp = ext4_get_group_info(ac->ac_sb, group);



	BUG_ON(cr < 0 || cr >= 4);

	BUG_ON(EXT4_MB_GRP_NEED_INIT(grp));



	/* We only do this if the grp has never been initialized */

	if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {

		int ret = ext4_mb_init_group(ac->ac_sb, group);

		if (ret)

			return 0;

	}



	free = grp->bb_free;

	fragments = grp->bb_fragments;
@@ -1843,17 +1886,16 @@ static int ext4_mb_good_group(struct ext4_allocation_context *ac, 
	case 0:

		BUG_ON(ac->ac_2order == 0);



		if (grp->bb_largest_free_order < ac->ac_2order)

			return 0;



		/* Avoid using the first bg of a flexgroup for data files */

		if ((ac->ac_flags & EXT4_MB_HINT_DATA) &&

		    (flex_size >= EXT4_FLEX_SIZE_DIR_ALLOC_SCHEME) &&

		    ((group % flex_size) == 0))

			return 0;



		bits = ac->ac_sb->s_blocksize_bits + 1;

		for (i = ac->ac_2order; i <= bits; i++)

			if (grp->bb_counters[i] > 0)

		return 1;

		break;

	case 1:

		if ((free / fragments) >= ac->ac_g_ex.fe_len)

			return 1;
@@ -2024,14 +2066,11 @@ repeat: 
		group = ac->ac_g_ex.fe_group;



		for (i = 0; i < ngroups; group++, i++) {

			struct ext4_group_info *grp;



			if (group == ngroups)

				group = 0;



			/* quick check to skip empty groups */

			grp = ext4_get_group_info(sb, group);

			if (grp->bb_free == 0)

			/* This now checks without needing the buddy page */

			if (!ext4_mb_good_group(ac, group, cr))

				continue;



			err = ext4_mb_load_buddy(sb, group, &e4b);
@@ -2039,8 +2078,12 @@ repeat: 
				goto out;



			ext4_lock_group(sb, group);



			/*

			 * We need to check again after locking the

			 * block group

			 */

			if (!ext4_mb_good_group(ac, group, cr)) {

				/* someone did allocation from this group */

				ext4_unlock_group(sb, group);

				ext4_mb_unload_buddy(&e4b);

				continue;
@@ -2253,6 +2296,7 @@ int ext4_mb_add_groupinfo(struct super_block *sb, ext4_group_t group, 
	INIT_LIST_HEAD(&meta_group_info[i]->bb_prealloc_list);

	init_rwsem(&meta_group_info[i]->alloc_sem);

	meta_group_info[i]->bb_free_root = RB_ROOT;

	meta_group_info[i]->bb_largest_free_order = -1;  /* uninit */



#ifdef DOUBLE_CHECK

	{

CRA Git | Maintained and supported by SUSTech CRA and CCSE