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Date:	Thu, 24 Jan 2008 13:26:14 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Theodore Ts'o" <tytso@....EDU>, linux-kernel@...r.kernel.org,
	alex@...sterfs.com, adilger@...sterfs.com, sandeen@...hat.com,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 41/49] ext4: Add multi block allocator for ext4

On Wed, Jan 23, 2008 at 02:07:27PM -0800, Andrew Morton wrote:
> > On Mon, 21 Jan 2008 22:02:20 -0500 "Theodore Ts'o" <tytso@....EDU> wrote:
> > From: Alex Tomas <alex@...sterfs.com>
> > 
> > Signed-off-by: Alex Tomas <alex@...sterfs.com>
> > Signed-off-by: Andreas Dilger <adilger@...sterfs.com>
> > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> > Signed-off-by: Eric Sandeen <sandeen@...hat.com>
> > Signed-off-by: "Theodore Ts'o" <tytso@....edu>
> >
> > ...
> >
> > +#if BITS_PER_LONG == 64
> > +#define mb_correct_addr_and_bit(bit, addr)		\
> > +{							\
> > +	bit += ((unsigned long) addr & 7UL) << 3;	\
> > +	addr = (void *) ((unsigned long) addr & ~7UL);	\
> > +}
> > +#elif BITS_PER_LONG == 32
> > +#define mb_correct_addr_and_bit(bit, addr)		\
> > +{							\
> > +	bit += ((unsigned long) addr & 3UL) << 3;	\
> > +	addr = (void *) ((unsigned long) addr & ~3UL);	\
> > +}
> > +#else
> > +#error "how many bits you are?!"
> > +#endif
> 
> Why do these exist?

Initial version on mballoc supported on x86 32 this was there to give
compile warning on 64 bit platform. I guess we can remove that now.
Or may be we can keep it as such because it is harmless.


> 
> > +static inline int mb_test_bit(int bit, void *addr)
> > +{
> > +	mb_correct_addr_and_bit(bit, addr);
> > +	return ext4_test_bit(bit, addr);
> > +}
> 
> ext2_test_bit() already handles bitnum > wordsize.
> 
> If mb_correct_addr_and_bit() is actually needed then some suitable comment
> would help.

ext4_test_bit on powerpc needs the addr to be 8 byte aligned. Othewise
it fails

> 
> > +static inline void mb_set_bit(int bit, void *addr)
> > +{
> > +	mb_correct_addr_and_bit(bit, addr);
> > +	ext4_set_bit(bit, addr);
> > +}
> > +
> > +static inline void mb_set_bit_atomic(spinlock_t *lock, int bit, void *addr)
> > +{
> > +	mb_correct_addr_and_bit(bit, addr);
> > +	ext4_set_bit_atomic(lock, bit, addr);
> > +}
> > +
> > +static inline void mb_clear_bit(int bit, void *addr)
> > +{
> > +	mb_correct_addr_and_bit(bit, addr);
> > +	ext4_clear_bit(bit, addr);
> > +}
> > +
> > +static inline void mb_clear_bit_atomic(spinlock_t *lock, int bit, void *addr)
> > +{
> > +	mb_correct_addr_and_bit(bit, addr);
> > +	ext4_clear_bit_atomic(lock, bit, addr);
> > +}
> > +
> > +static inline void *mb_find_buddy(struct ext4_buddy *e4b, int order, int *max)
> 
> uninlining this will save about eighty squigabytes of text.

Fixed


> 
> Please review all of ext4/jbd2 with a view to removig unnecessary and wrong
> inlings.
> 
> > +{
> > +	char *bb;
> > +
> > +	/* FIXME!! is this needed */
> > +	BUG_ON(EXT4_MB_BITMAP(e4b) == EXT4_MB_BUDDY(e4b));
> > +	BUG_ON(max == NULL);
> > +
> > +	if (order > e4b->bd_blkbits + 1) {
> > +		*max = 0;
> > +		return NULL;
> > +	}
> > +
> > +	/* at order 0 we see each particular block */
> > +	*max = 1 << (e4b->bd_blkbits + 3);
> > +	if (order == 0)
> > +		return EXT4_MB_BITMAP(e4b);
> > +
> > +	bb = EXT4_MB_BUDDY(e4b) + EXT4_SB(e4b->bd_sb)->s_mb_offsets[order];
> > +	*max = EXT4_SB(e4b->bd_sb)->s_mb_maxs[order];
> > +
> > +	return bb;
> > +}
> > +
> >
> > ...
> >
> > +#else
> > +#define mb_free_blocks_double(a, b, c, d)
> > +#define mb_mark_used_double(a, b, c)
> > +#define mb_cmp_bitmaps(a, b)
> > +#endif
> 
> Please use the do{}while(0) thing.  Or, better, proper C functions which
> have typechecking (unless this will cause undefined-var compile errors,
> which happens sometimes)

makde static inline void.

> 
> > +/* find most significant bit */
> > +static int fmsb(unsigned short word)
> > +{
> > +	int order;
> > +
> > +	if (word > 255) {
> > +		order = 7;
> > +		word >>= 8;
> > +	} else {
> > +		order = -1;
> > +	}
> > +
> > +	do {
> > +		order++;
> > +		word >>= 1;
> > +	} while (word != 0);
> > +
> > +	return order;
> > +}
> 
> Did we just reinvent fls()?

replaced by fls.

> 
> > +/* FIXME!! need more doc */
> > +static void ext4_mb_mark_free_simple(struct super_block *sb,
> > +				void *buddy, unsigned first, int len,
> > +					struct ext4_group_info *grp)
> > +{
> > +	struct ext4_sb_info *sbi = EXT4_SB(sb);
> > +	unsigned short min;
> > +	unsigned short max;
> > +	unsigned short chunk;
> > +	unsigned short border;
> > +
> > +	BUG_ON(len >= EXT4_BLOCKS_PER_GROUP(sb));
> > +
> > +	border = 2 << sb->s_blocksize_bits;
> 
> Won't this explode with >= 32k blocksize?
> 
> > +	while (len > 0) {
> > +		/* find how many blocks can be covered since this position */
> > +		max = ffs(first | border) - 1;
> > +
> > +		/* find how many blocks of power 2 we need to mark */
> > +		min = fmsb(len);
> > +
> > +		if (max < min)
> > +			min = max;
> > +		chunk = 1 << min;
> > +
> > +		/* mark multiblock chunks only */
> > +		grp->bb_counters[min]++;
> > +		if (min > 0)
> > +			mb_clear_bit(first >> min,
> > +				     buddy + sbi->s_mb_offsets[min]);
> > +
> > +		len -= chunk;
> > +		first += chunk;
> > +	}
> > +}
> > +
> > 
> > ...
> >
> > +static int ext4_mb_init_cache(struct page *page, char *incore)
> > +{
> > +	int blocksize;
> > +	int blocks_per_page;
> > +	int groups_per_page;
> > +	int err = 0;
> > +	int i;
> > +	ext4_group_t first_group;
> > +	int first_block;
> > +	struct super_block *sb;
> > +	struct buffer_head *bhs;
> > +	struct buffer_head **bh;
> > +	struct inode *inode;
> > +	char *data;
> > +	char *bitmap;
> > +
> > +	mb_debug("init page %lu\n", page->index);
> > +
> > +	inode = page->mapping->host;
> > +	sb = inode->i_sb;
> > +	blocksize = 1 << inode->i_blkbits;
> > +	blocks_per_page = PAGE_CACHE_SIZE / blocksize;
> > +
> > +	groups_per_page = blocks_per_page >> 1;
> > +	if (groups_per_page == 0)
> > +		groups_per_page = 1;
> > +
> > +	/* allocate buffer_heads to read bitmaps */
> > +	if (groups_per_page > 1) {
> > +		err = -ENOMEM;
> > +		i = sizeof(struct buffer_head *) * groups_per_page;
> > +		bh = kmalloc(i, GFP_NOFS);
> > +		if (bh == NULL)
> > +			goto out;
> > +		memset(bh, 0, i);
> 
> kzalloc()

Fixed

> 
> > +	} else
> > +		bh = &bhs;
> > +
> > +	first_group = page->index * blocks_per_page / 2;
> > +
> > +	/* read all groups the page covers into the cache */
> > +	for (i = 0; i < groups_per_page; i++) {
> > +		struct ext4_group_desc *desc;
> > +
> > +		if (first_group + i >= EXT4_SB(sb)->s_groups_count)
> > +			break;
> > +
> > +		err = -EIO;
> > +		desc = ext4_get_group_desc(sb, first_group + i, NULL);
> > +		if (desc == NULL)
> > +			goto out;
> > +
> > +		err = -ENOMEM;
> > +		bh[i] = sb_getblk(sb, ext4_block_bitmap(sb, desc));
> > +		if (bh[i] == NULL)
> > +			goto out;
> > +
> > +		if (buffer_uptodate(bh[i]))
> > +			continue;
> > +
> > +		lock_buffer(bh[i]);
> > +		if (buffer_uptodate(bh[i])) {
> > +			unlock_buffer(bh[i]);
> > +			continue;
> > +		}
> 
> Didn't we just add a helper in fs/buffer.c to do this?
> 

Fixed


> > +		if (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
> > +			ext4_init_block_bitmap(sb, bh[i],
> > +						first_group + i, desc);
> > +			set_buffer_uptodate(bh[i]);
> > +			unlock_buffer(bh[i]);
> > +			continue;
> > +		}
> > +		get_bh(bh[i]);
> > +		bh[i]->b_end_io = end_buffer_read_sync;

[... snip... ]
> > +
> > +			/* set incore so that the buddy information can be
> > +			 * generated using this
> > +			 */
> > +			incore = data;
> > +		}
> > +	}
> > +	SetPageUptodate(page);
> 
> Is the page locked here?


The page is locked via find_or_create_page

> 
> > +out:
> > +	if (bh) {
> > +		for (i = 0; i < groups_per_page && bh[i]; i++)
> > +			brelse(bh[i]);
> 
> put_bh()
> 
> > +		if (bh != &bhs)
> > +			kfree(bh);
> > +	}
> > +	return err;
> > +}
> > +
> >
> > ...
> >
> > +static void mb_set_bits(spinlock_t *lock, void *bm, int cur, int len)
> > +{
> > +	__u32 *addr;
> > +
> > +	len = cur + len;
> > +	while (cur < len) {
> > +		if ((cur & 31) == 0 && (len - cur) >= 32) {
> > +			/* fast path: clear whole word at once */
> 
> s/clear/set/

Fixed

> 
> > +			addr = bm + (cur >> 3);
> > +			*addr = 0xffffffff;
> > +			cur += 32;
> > +			continue;
> > +		}
> > +		mb_set_bit_atomic(lock, cur, bm);
> > +		cur++;
> > +	}
> > +}
> > +
> >
> > ...
> >
> > +static void ext4_mb_generate_from_pa(struct super_block *sb, void *bitmap,
> > +					ext4_group_t group)
> > +{
> > +	struct ext4_group_info *grp = ext4_get_group_info(sb, group);
> > +	struct ext4_prealloc_space *pa;
> > +	struct list_head *cur;
> > +	ext4_group_t groupnr;
> > +	ext4_grpblk_t start;
> > +	int preallocated = 0;
> > +	int count = 0;
> > +	int len;
> > +
> > +	/* all form of preallocation discards first load group,
> > +	 * so the only competing code is preallocation use.
> > +	 * we don't need any locking here
> > +	 * notice we do NOT ignore preallocations with pa_deleted
> > +	 * otherwise we could leave used blocks available for
> > +	 * allocation in buddy when concurrent ext4_mb_put_pa()
> > +	 * is dropping preallocation
> > +	 */
> > +	list_for_each_rcu(cur, &grp->bb_prealloc_list) {
> > +		pa = list_entry(cur, struct ext4_prealloc_space, pa_group_list);
> > +		spin_lock(&pa->pa_lock);
> > +		ext4_get_group_no_and_offset(sb, pa->pa_pstart,
> > +					     &groupnr, &start);
> > +		len = pa->pa_len;
> > +		spin_unlock(&pa->pa_lock);
> > +		if (unlikely(len == 0))
> > +			continue;
> > +		BUG_ON(groupnr != group);
> > +		mb_set_bits(sb_bgl_lock(EXT4_SB(sb), group),
> > +						bitmap, start, len);
> > +		preallocated += len;
> > +		count++;
> > +	}
> 
> Seems to be missing rcu_read_lock()
> 


bb_prealloc_list  is actually modified under ext4_group_lock. So it is
not actually rcu. I this we should be using list_for_each there.
The rcu managed list are i_prealloc_list and lg_prealloc_list


> > +	mb_debug("prellocated %u for group %lu\n", preallocated, group);
> > +}
> > +
> > +static void ext4_mb_pa_callback(struct rcu_head *head)
> > +{
> > +	struct ext4_prealloc_space *pa;
> > +	pa = container_of(head, struct ext4_prealloc_space, u.pa_rcu);
> > +	kmem_cache_free(ext4_pspace_cachep, pa);
> > +}
> > +#define mb_call_rcu(__pa)	call_rcu(&(__pa)->u.pa_rcu, ext4_mb_pa_callback)
> 
> Is there any reason why this had to be implemented as a macro?

Fixed

> 
> >
> > ...
> >
> > +static int ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
> > +{
> > +	struct super_block *sb = ac->ac_sb;
> > +	struct ext4_prealloc_space *pa;
> > +	struct ext4_group_info *grp;
> > +	struct ext4_inode_info *ei;
> > +
> > +	/* preallocate only when found space is larger then requested */
> > +	BUG_ON(ac->ac_o_ex.fe_len >= ac->ac_b_ex.fe_len);
> > +	BUG_ON(ac->ac_status != AC_STATUS_FOUND);
> > +	BUG_ON(!S_ISREG(ac->ac_inode->i_mode));
> > +
> > +	pa = kmem_cache_alloc(ext4_pspace_cachep, GFP_NOFS);
> 
> Do all the GFP_NOFS's in this code really need to be GFP_NOFS?
> 
> > +	if (pa == NULL)
> > +		return -ENOMEM;
> > +	ext4_lock_group(sb, ac->ac_b_ex.fe_group);

....

> > +	list_add_rcu(&pa->pa_group_list, &grp->bb_prealloc_list);
> > +	ext4_unlock_group(sb, ac->ac_b_ex.fe_group);
> > +
> > +	spin_lock(pa->pa_obj_lock);
> > +	list_add_rcu(&pa->pa_inode_list, &ei->i_prealloc_list);
> > +	spin_unlock(pa->pa_obj_lock);
> 
> hm.  Strange to see list_add_rcu() inside spinlock like this.

Few lines above we have
pa->pa_obj_lock = &ei->i_prealloc_lock;
So the spin_lock is there to prevent mutiple cpu's adding to the
prealloc list together.


> 
> > +	return 0;
> > +}
> > +
> >
> > ...
> >
> > +static int ext4_mb_discard_group_preallocations(struct super_block *sb,
> > +					ext4_group_t group, int needed)
> > +{
> > +	struct ext4_group_info *grp = ext4_get_group_info(sb, group);
> > +	struct buffer_head *bitmap_bh = NULL;
> > +	struct ext4_prealloc_space *pa, *tmp;
> > +	struct list_head list;
> > +	struct ext4_buddy e4b;
> > +	int err;
> > +	int busy = 0;
> > +	int free = 0;
> > +		/* seems this one can be freed ... */

....

> > +		pa->pa_deleted = 1;
> > +
> > +		/* we can trust pa_free ... */
> > +		free += pa->pa_free;
> > +
> > +		spin_unlock(&pa->pa_lock);
> > +
> > +		list_del_rcu(&pa->pa_group_list);
> > +		list_add(&pa->u.pa_tmp_list, &list);
> > +	}
> 
> Strange to see rcu operations outside rcu_read_lock().

That need not be actually list_del_rcu. As i stated above that is
holding the bb_prealloc_list. It is updated under ext4_group_lock



> 
> > +	/* if we still need more blocks and some PAs were used, try again */
> > +	if (free < needed && busy) {
> > +		busy = 0;
> > +		ext4_unlock_group(sb, group);
> > +		/*
> > +		 * Yield the CPU here so that we don't get soft lockup
> > +		 * in non preempt case.
> > +		 */
> > +		yield();
> 
> argh, no, yield() is basically unusable.  schedule_timeout(1) is preferable.

I actually schedule_timeout(HZ); This was actually a bug fix a soft
lockup happening when we were running non preemptible kernel. Well we
just want to make sure the high priority watchdog thread gets a chance
to run. And if there are no high priority threads we ourself would like
to run. My understanding was yield is the right choice there.


> 
> Please test this code whe there are lots of cpu-intensive tasks running.
> 
> > +		goto repeat;
> > +	}
> > +
> > +	/* found anything to free? */
> > +	if (list_empty(&list)) {
> > +		BUG_ON(free != 0);
> > +		goto out;
> > +	}
> > +
> > +	/* now free all selected PAs */
> > +		if (atomic_read(&pa->pa_count)) {
> > +			/* this shouldn't happen often - nobody should

.....


> > +			 * use preallocation while we're discarding it */
> > +			spin_unlock(&pa->pa_lock);
> > +			spin_unlock(&ei->i_prealloc_lock);
> > +			printk(KERN_ERR "uh-oh! used pa while discarding\n");
> > +			dump_stack();
> 
> WARN_ON(1) would be more conventional.

Fixed

> 
> > +			current->state = TASK_UNINTERRUPTIBLE;
> > +			schedule_timeout(HZ);
> 
> schedule_timeout_uninterruptible()
> 

Fixed

> > +			goto repeat;
> > +
> > +		}
> > +		if (pa->pa_deleted == 0) {
> > +			pa->pa_deleted = 1;
> > +			spin_unlock(&pa->pa_lock);
> > +			list_del_rcu(&pa->pa_inode_list);
> > +			list_add(&pa->u.pa_tmp_list, &list);
> > +			continue;
> > +		}
> > +
> > +		/* someone is deleting pa right now */
> > +		spin_unlock(&pa->pa_lock);
> > +		spin_unlock(&ei->i_prealloc_lock);
> > +
> > +		/* we have to wait here because pa_deleted
> > +		 * doesn't mean pa is already unlinked from
> > +		 * the list. as we might be called from
> > +		 * ->clear_inode() the inode will get freed
> > +		 * and concurrent thread which is unlinking
> > +		 * pa from inode's list may access already
> > +		 * freed memory, bad-bad-bad */
> > +
> > +		/* XXX: if this happens too often, we can
> > +		 * add a flag to force wait only in case
> > +		 * of ->clear_inode(), but not in case of
> > +		 * regular truncate */
> > +		current->state = TASK_UNINTERRUPTIBLE;
> > +		schedule_timeout(HZ);
> 
> ditto
> 

Fixed

> > +		goto repeat;
> > +	}
> > +	spin_unlock(&ei->i_prealloc_lock);
> > +
> > +	list_for_each_entry_safe(pa, tmp, &list, u.pa_tmp_list) {
> > +		BUG_ON(pa->pa_linear != 0);
> > +		ext4_get_group_no_and_offset(sb, pa->pa_pstart, &group, NULL);
> > +
> > +		err = ext4_mb_load_buddy(sb, group, &e4b);
> > +		BUG_ON(err != 0); /* error handling here */
> > +
> > +		bitmap_bh = read_block_bitmap(sb, group);
> > +		if (bitmap_bh == NULL) {
> > +			/* error handling here */
> > +			ext4_mb_release_desc(&e4b);
> > +			BUG_ON(bitmap_bh == NULL);
> > +		}
> > +
> > +		ext4_lock_group(sb, group);
> > +		list_del_rcu(&pa->pa_group_list);
> > +		ext4_mb_release_inode_pa(&e4b, bitmap_bh, pa);
> > +		ext4_unlock_group(sb, group);
> > +
> > +		ext4_mb_release_desc(&e4b);
> > +		brelse(bitmap_bh);
> > +
> > +		list_del(&pa->u.pa_tmp_list);
> > +		mb_call_rcu(pa);
> > +	}
> > +}
> 
> Would be nice to ask Paul to review all the rcu usage in here.  It looks odd.
> 

Will add Paul to the CC

> >
> > ...
> >
> > +#else
> > +#define ext4_mb_show_ac(x)
> > +#endif
> 
> static inlined C functions are preferred (+1e6 dittoes)

Fixed

> 
> > +/*
> > + * We use locality group preallocation for small size file. The size of the
> > + * file is determined by the current size or the resulting size after
> > + * allocation which ever is larger
> > + *
> > + * One can tune this size via /proc/fs/ext4/<partition>/stream_req
> > + */
> > +static void ext4_mb_group_or_file(struct ext4_allocation_context *ac)
> > +{
> > +	struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
> > +	int bsbits = ac->ac_sb->s_blocksize_bits;
> > +	loff_t size, isize;
> > +
> > +	if (!(ac->ac_flags & EXT4_MB_HINT_DATA))
> > +		return;
> > +
> > +	size = ac->ac_o_ex.fe_logical + ac->ac_o_ex.fe_len;
> > +	isize = i_size_read(ac->ac_inode) >> bsbits;
> > +	if (size < isize)
> > +		size = isize;
> 
> min()?
> 

updated as size = max(size, isize);


> > +	/* don't use group allocation for large files */
> > +	if (size >= sbi->s_mb_stream_request)
> > +		return;
> > +
> > +	if (unlikely(ac->ac_flags & EXT4_MB_HINT_GOAL_ONLY))
> > +		return;
> > +
> > +	BUG_ON(ac->ac_lg != NULL);
> > +	ac->ac_lg = &sbi->s_locality_groups[get_cpu()];
> > +	put_cpu();
> 
> Strange-looking code.  I'd be interested in a description of the per-cou
> design here.

I added the below doc


/*
 * locality group prealloc space are per cpu. The reason for
 * having  per cpu locality group is to reduce the contention
 * between block  request from multiple CPUs.
 */




> 
> > +	/* we're going to use group allocation */
> > +	ac->ac_flags |= EXT4_MB_HINT_GROUP_ALLOC;
> > +
> > +	/* serialize all allocations in the group */
> > +	down(&ac->ac_lg->lg_sem);
> 
> This should be a mutex, shouldn't it?
> 

converted to mutex


> > +}
> > +
> >
> > ...
> >
> > +static int ext4_mb_free_metadata(handle_t *handle, struct ext4_buddy *e4b,
> > +			  ext4_group_t group, ext4_grpblk_t block, int count)
> > +{
> > +	struct ext4_group_info *db = e4b->bd_info;
> > +	struct super_block *sb = e4b->bd_sb;
> > +	struct ext4_sb_info *sbi = EXT4_SB(sb);
> > +	struct ext4_free_metadata *md;
> > +	int i;
> > +
> > +	BUG_ON(e4b->bd_bitmap_page == NULL);
> > +	BUG_ON(e4b->bd_buddy_page == NULL);
> > +
> > +	ext4_lock_group(sb, group);
> > +	for (i = 0; i < count; i++) {
> > +		md = db->bb_md_cur;
> > +		if (md && db->bb_tid != handle->h_transaction->t_tid) {
> > +			db->bb_md_cur = NULL;
> > +			md = NULL;
> > +		}
> > +
> > +		if (md == NULL) {
> > +			ext4_unlock_group(sb, group);
> > +			md = kmalloc(sizeof(*md), GFP_KERNEL);
> 
> Why was this one not GFP_NOFS?
> 
> > +			if (md == NULL)
> > +				return -ENOMEM;
> 
> Did we just leak some memory?
> 

No the data is allocated to carry information regarding the free blocks.


> > +			md->num = 0;
> > +			md->group = group;
> > +
> > +			ext4_lock_group(sb, group);
> > +			if (db->bb_md_cur == NULL) {
> > +				spin_lock(&sbi->s_md_lock);
> > +				list_add(&md->list, &sbi->s_active_transaction);
> > +				spin_unlock(&sbi->s_md_lock);
> > +				/* protect buddy cache from being freed,
> > +				 * otherwise we'll refresh it from
> > +				 * on-disk bitmap and lose not-yet-available
> > +				 * blocks */
> > +				page_cache_get(e4b->bd_buddy_page);
> > +				page_cache_get(e4b->bd_bitmap_page);
> > +				db->bb_md_cur = md;
> > +				db->bb_tid = handle->h_transaction->t_tid;
> > +				mb_debug("new md 0x%p for group %lu\n",
> > +						md, md->group);
> > +			} else {
> > +				kfree(md);
> > +				md = db->bb_md_cur;
> > +			}
> > +		}
> > +
> > +		BUG_ON(md->num >= EXT4_BB_MAX_BLOCKS);
> > +		md->blocks[md->num] = block + i;
> > +		md->num++;
> > +		if (md->num == EXT4_BB_MAX_BLOCKS) {
> > +			/* no more space, put full container on a sb's list */
> > +			db->bb_md_cur = NULL;
> > +		}
> > +	}
> > +	ext4_unlock_group(sb, group);
> > +	return 0;
> > +}
> > +
> >
> > ...
> >
> > +		case Opt_mballoc:
> > +			set_opt(sbi->s_mount_opt, MBALLOC);
> > +			break;
> > +		case Opt_nomballoc:
> > +			clear_opt(sbi->s_mount_opt, MBALLOC);
> > +			break;
> > +		case Opt_stripe:
> > +			if (match_int(&args[0], &option))
> > +				return 0;
> > +			if (option < 0)
> > +				return 0;
> > +			sbi->s_stripe = option;
> > +			break;
> 
> These appear to be undocumented.

Updated


> 
> >  		default:
> >  			printk (KERN_ERR
> >  				"EXT4-fs: Unrecognized mount option \"%s\" "
> > @@ -1742,6 +1762,33 @@ static ext4_fsblk_t descriptor_loc(struct super_block *sb,
> >  	return (has_super + ext4_group_first_block_no(sb, bg));
> >  }
> >  
> > +/**
> > + * ext4_get_stripe_size: Get the stripe size.
> > + * @sbi: In memory super block info
> > + *
> > + * If we have specified it via mount option, then
> > + * use the mount option value. If the value specified at mount time is
> > + * greater than the blocks per group use the super block value.
> > + * If the super block value is greater than blocks per group return 0.
> > + * Allocator needs it be less than blocks per group.
> > + *
> > + */
> > +static unsigned long ext4_get_stripe_size(struct ext4_sb_info *sbi)
> > +{
> > +	unsigned long stride = le16_to_cpu(sbi->s_es->s_raid_stride);
> > +	unsigned long stripe_width =
> > +			le32_to_cpu(sbi->s_es->s_raid_stripe_width);
> > +
> > +	if (sbi->s_stripe && sbi->s_stripe <= sbi->s_blocks_per_group) {
> > +		return sbi->s_stripe;
> > +	} else if (stripe_width <= sbi->s_blocks_per_group) {
> > +		return stripe_width;
> > +	} else if (stride <= sbi->s_blocks_per_group) {
> > +		return stride;
> > +	}
> 
> unneeded braces.

I was thinking it is ok these days. checkpatch didn't warn and i had
multiple else if. I could remove those else if


> 
> > +	return 0;
> > +}
> >  
> >  ...
> >
> > +static inline
> > +struct ext4_group_info *ext4_get_group_info(struct super_block *sb,
> > +							ext4_group_t group)
> > +{
> > +	 struct ext4_group_info ***grp_info;
> > +	 long indexv, indexh;
> > +	 grp_info = EXT4_SB(sb)->s_group_info;
> > +	 indexv = group >> (EXT4_DESC_PER_BLOCK_BITS(sb));
> > +	 indexh = group & ((EXT4_DESC_PER_BLOCK(sb)) - 1);
> > +	 return grp_info[indexv][indexh];
> > +}
> 
> This should be uninlined.
> 
> 
> 
> Gosh what a lot of code.  Is it faster?

Performance numbers with compile bench http://ext4.wiki.kernel.org/index.php/Performance_results
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