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Message-Id: <20081104173215.92ac3585.akpm@linux-foundation.org>
Date: Tue, 4 Nov 2008 17:32:15 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Mingming Cao <cmm@...ibm.com>
Cc: jack@...e.cz, tytso@....edu, linux-ext4@...r.kernel.org,
linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH V2 3/3] ext4: quota handling for delayed allocation
On Fri, 31 Oct 2008 14:27:31 -0700
Mingming Cao <cmm@...ibm.com> wrote:
> ext4: quota reservation for delayed allocation
>
> Uses quota reservation/claim/release to handle quota properly for delayed
> allocation in the three steps: 1) quotas are reserved when data being copied
> to cache when block allocation is defered 2) when new blocks are allocated.
> reserved quotas are converted to the real allocated quota, 2) over-booked
> quotas for metadata blocks are released back.
>
>
> Signed-off-by: Mingming Cao <cmm@...ibm.com>
> ---
> fs/ext4/inode.c | 25 ++++++++++++++++++++++++-
> fs/ext4/mballoc.c | 18 +++++++++---------
> fs/ext4/super.c | 2 ++
> 3 files changed, 35 insertions(+), 10 deletions(-)
>
> Index: linux-2.6.28-rc2/fs/ext4/inode.c
> ===================================================================
> --- linux-2.6.28-rc2.orig/fs/ext4/inode.c 2008-10-29 13:26:55.000000000 -0700
> +++ linux-2.6.28-rc2/fs/ext4/inode.c 2008-10-30 14:25:47.000000000 -0700
> @@ -994,7 +994,9 @@ static void ext4_da_update_reserve_space
> {
> struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
> int total, mdb, mdb_free;
> + int claim_quota, free_quota = 0;
>
> + claim_quota = used;
> spin_lock(&EXT4_I(inode)->i_block_reservation_lock);
> /* recalculate the number of metablocks still need to be reserved */
> total = EXT4_I(inode)->i_reserved_data_blocks - used;
> @@ -1007,6 +1009,8 @@ static void ext4_da_update_reserve_space
> if (mdb_free) {
> /* Account for allocated meta_blocks */
> mdb_free -= EXT4_I(inode)->i_allocated_meta_blocks;
> + free_quota = mdb_free;
> + claim_quota += EXT4_I(inode)->i_allocated_meta_blocks;
>
> /* update fs dirty blocks counter */
> percpu_counter_sub(&sbi->s_dirtyblocks_counter, mdb_free);
> @@ -1017,8 +1021,14 @@ static void ext4_da_update_reserve_space
> /* update per-inode reservations */
> BUG_ON(used > EXT4_I(inode)->i_reserved_data_blocks);
> EXT4_I(inode)->i_reserved_data_blocks -= used;
> -
> spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
> +
> + /*
> + * free those over-booking quota for metadata blocks
> + */
> +
> + if (free_quota)
> + DQUOT_RELEASE_RSV_BLOCK(inode, free_quota);
> }
>
> /*
> @@ -1514,8 +1524,8 @@ static int ext4_journalled_write_end(str
> static int ext4_da_reserve_space(struct inode *inode, int nrblocks)
> {
> int retries = 0;
> - struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
> - unsigned long md_needed, mdblocks, total = 0;
> + struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
> + unsigned long md_needed, mdblocks, total = 0;
>
> /*
> * recalculate the amount of metadata blocks to reserve
> @@ -1531,12 +1541,23 @@ repeat:
> md_needed = mdblocks - EXT4_I(inode)->i_reserved_meta_blocks;
> total = md_needed + nrblocks;
>
> + /*
> + * Make quota reservation here, to prevent quota overflow
> + * later.Real quota accounting is done at pages writeout
> + * time
"Make the quota reservation here to prevent quota overflow later. Real
quota accounting is performed and page writeout time."
> + */
> + if (DQUOT_RESERVE_BLOCK(inode, total)) {
> + spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
> + return -EDQUOT;
> + }
Mangled whitespace. checkpatch seems to miss this (but you didn't run
checkpatch anyway. Please do so?)
> if (ext4_claim_free_blocks(sbi, total)) {
> spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
> if (ext4_should_retry_alloc(inode->i_sb, &retries)) {
> yield();
> goto repeat;
> }
> + DQUOT_RELEASE_RSV_BLOCK(inode,total);
> return -ENOSPC;
> }
> EXT4_I(inode)->i_reserved_data_blocks += nrblocks;
> @@ -1590,6 +1611,8 @@ static void ext4_da_release_space(struct
> BUG_ON(mdb > EXT4_I(inode)->i_reserved_meta_blocks);
> EXT4_I(inode)->i_reserved_meta_blocks = mdb;
> spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
> +
> + DQUOT_RELEASE_RSV_BLOCK(inode, release);
> }
DQUOT_RESERVE_BLOCK needs i_block_reservation_lock? And
DQUOT_RELEASE_RSV_BLOCK does not? Seems peculiar.
Please see if we can avoid the bad multiple-return-statements?
This function evaluates EXT4_I(inode) many times. I'd suggest that you
look at caching the result of that expression in a local variable, see
if that results in improved code generation on common architectures.
> static void ext4_da_page_release_reservation(struct page *page,
> Index: linux-2.6.28-rc2/fs/ext4/super.c
> ===================================================================
> --- linux-2.6.28-rc2.orig/fs/ext4/super.c 2008-10-29 13:26:55.000000000 -0700
> +++ linux-2.6.28-rc2/fs/ext4/super.c 2008-10-29 14:00:27.000000000 -0700
> @@ -795,6 +795,9 @@ static struct dquot_operations ext4_quot
> .initialize = ext4_dquot_initialize,
> .drop = ext4_dquot_drop,
> .alloc_space = dquot_alloc_space,
> + .reserve_space = dquot_reserve_space,
> + .claim_space = dquot_claim_space,
> + .release_rsv = dquot_release_reserved_space,
> .alloc_inode = dquot_alloc_inode,
> .free_space = dquot_free_space,
> .free_inode = dquot_free_inode,
> Index: linux-2.6.28-rc2/fs/ext4/mballoc.c
> ===================================================================
> --- linux-2.6.28-rc2.orig/fs/ext4/mballoc.c 2008-10-29 13:26:55.000000000 -0700
> +++ linux-2.6.28-rc2/fs/ext4/mballoc.c 2008-10-30 14:30:39.000000000 -0700
> @@ -2887,9 +2887,11 @@ ext4_mb_mark_diskspace_used(struct ext4_
> if (!(ac->ac_flags & EXT4_MB_DELALLOC_RESERVED))
> /* release all the reserved blocks if non delalloc */
> percpu_counter_sub(&sbi->s_dirtyblocks_counter, reserv_blks);
> - else
> + else {
> percpu_counter_sub(&sbi->s_dirtyblocks_counter,
> ac->ac_b_ex.fe_len);
> + DQUOT_CLAIM_BLOCK(ac->ac_inode, ac->ac_b_ex.fe_len);
> + }
>
> if (sbi->s_log_groups_per_flex) {
> ext4_group_t flex_group = ext4_flex_group(sbi,
> @@ -4286,15 +4288,24 @@ ext4_fsblk_t ext4_mb_new_blocks(handle_t
> struct ext4_sb_info *sbi;
> struct super_block *sb;
> ext4_fsblk_t block = 0;
> - unsigned long inquota;
> + unsigned long inquota = 0;
> unsigned long reserv_blks = 0;
>
> sb = ar->inode->i_sb;
> sbi = EXT4_SB(sb);
>
> - if (!EXT4_I(ar->inode)->i_delalloc_reserved_flag) {
> + /*
> + * For delayed allocation, we could skip the ENOSPC and
> + * EDQUOT check, as blocks and quotas have been already
> + * reserved when data being copied to cache
"when data was copied into pagecache"?
> + */
> + if (EXT4_I(ar->inode)->i_delalloc_reserved_flag)
> + ar->flags |= EXT4_MB_DELALLOC_RESERVED;
> + else {
> /*
> - * With delalloc we already reserved the blocks
> + * Without delayed allocation we need to verify
> + * there is enough free blocks to do block allocation
> + * and under the quota limits
I don't understand the "and under the quota limits" bit. What is this
referring to?
The comment needs a bit of attention.
> */
> while (ar->len && ext4_claim_free_blocks(sbi, ar->len)) {
> /* let others to free the space */
> @@ -4306,19 +4317,16 @@ ext4_fsblk_t ext4_mb_new_blocks(handle_t
> return 0;
> }
> reserv_blks = ar->len;
> + while (ar->len && DQUOT_ALLOC_BLOCK(ar->inode, ar->len)) {
> + ar->flags |= EXT4_MB_HINT_NOPREALLOC;
> + ar->len--;
> + }
What's this doing? Trying increasingly small quota allocations until
one of them succeeds? This sounds like a good way to burn up a large
number of cycles.
Isn't there some way we can be smarter about this? Surely the quota
layer knows exactly how many blocks we can reserve.
> + if (ar->len == 0) {
> + *errp = -EDQUOT;
> + return 0;
> + }
> + inquota = ar->len;
> }
> - while (ar->len && DQUOT_ALLOC_BLOCK(ar->inode, ar->len)) {
> - ar->flags |= EXT4_MB_HINT_NOPREALLOC;
> - ar->len--;
> - }
Oh, it already sucked :)
> - if (ar->len == 0) {
> - *errp = -EDQUOT;
> - return 0;
> - }
> - inquota = ar->len;
> -
> - if (EXT4_I(ar->inode)->i_delalloc_reserved_flag)
> - ar->flags |= EXT4_MB_DELALLOC_RESERVED;
>
> ac = kmem_cache_alloc(ext4_ac_cachep, GFP_NOFS);
> if (!ac) {
> @@ -4380,7 +4388,7 @@ repeat:
> out2:
> kmem_cache_free(ext4_ac_cachep, ac);
> out1:
> - if (ar->len < inquota)
> + if (inquota && ar->len < inquota)
> DQUOT_FREE_BLOCK(ar->inode, inquota - ar->len);
>
> return block;
>
--
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