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Message-ID: <518cd8d7-394c-4b19-a0b9-f73219c621de@linux.alibaba.com>
Date: Thu, 17 Apr 2025 19:11:23 +0800
From: Joseph Qi <joseph.qi@...ux.alibaba.com>
To: Heming Zhao <heming.zhao@...e.com>, akpm <akpm@...ux-foundation.org>
Cc: ocfs2-devel@...ts.linux.dev, linux-kernel@...r.kernel.org,
gautham.ananthakrishna@...cle.com
Subject: Re: [PATCH v2 1/1] ocfs2: fix the issue with discontiguous allocation
in the global_bitmap
On 2025/4/14 14:01, Heming Zhao wrote:
> The commit 4eb7b93e0310 ("ocfs2: improve write IO performance when
> fragmentation is high") introduced another regression.
>
> The following ocfs2-test case can trigger this issue:
>> discontig_runner.sh => activate_discontig_bg.sh => resv_unwritten:
>> ${RESV_UNWRITTEN_BIN} -f ${WORK_PLACE}/large_testfile -s 0 -l \
>> $((${FILE_MAJOR_SIZE_M}*1024*1024))
>
> In my env, test disk size (by "fdisk -l <dev>"):
>> 53687091200 bytes, 104857600 sectors.
>
> Above command is:
>> /usr/local/ocfs2-test/bin/resv_unwritten -f \
>> /mnt/ocfs2/ocfs2-activate-discontig-bg-dir/large_testfile -s 0 -l \
>> 53187969024
>
> Error log:
>> [*] Reserve 50724M space for a LARGE file, reserve 200M space for future test.
>> ioctl error 28: "No space left on device"
>> resv allocation failed Unknown error -1
>> reserve unwritten region from 0 to 53187969024.
>
> Call flow:
> __ocfs2_change_file_space //by ioctl OCFS2_IOC_RESVSP64
> ocfs2_allocate_unwritten_extents //start:0 len:53187969024
> while()
> + ocfs2_get_clusters //cpos:0, alloc_size:1623168 (cluster number)
> + ocfs2_extend_allocation
> + ocfs2_lock_allocators
> | + choose OCFS2_AC_USE_MAIN & ocfs2_cluster_group_search
> |
> + ocfs2_add_inode_data
> ocfs2_add_clusters_in_btree
> __ocfs2_claim_clusters
> ocfs2_claim_suballoc_bits
> + During the allocation of the final part of the large file
> (after ~47GB), no chain had the required contiguous
> bits_wanted. Consequently, the allocation failed.
>
> How to fix:
> When OCFS2 is encountering fragmented allocation, the file system should
> stop attempting bits_wanted contiguous allocation and instead provide the
> largest available contiguous free bits from the cluster groups.
>
> Reported-by: Gautham Ananthakrishna <gautham.ananthakrishna@...cle.com>
> Signed-off-by: Heming Zhao <heming.zhao@...e.com>
> Fixes: 4eb7b93e0310 ("ocfs2: improve write IO performance when fragmentation is high")
Reviewed-by: Joseph Qi <joseph.qi@...ux.alibaba.com>
> ---
> fs/ocfs2/suballoc.c | 38 ++++++++++++++++++++++++++++++++------
> fs/ocfs2/suballoc.h | 1 +
> 2 files changed, 33 insertions(+), 6 deletions(-)
>
> diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c
> index f7b483f0de2a..6ac4dcd54588 100644
> --- a/fs/ocfs2/suballoc.c
> +++ b/fs/ocfs2/suballoc.c
> @@ -698,10 +698,12 @@ static int ocfs2_block_group_alloc(struct ocfs2_super *osb,
>
> bg_bh = ocfs2_block_group_alloc_contig(osb, handle, alloc_inode,
> ac, cl);
> - if (PTR_ERR(bg_bh) == -ENOSPC)
> + if (PTR_ERR(bg_bh) == -ENOSPC) {
> + ac->ac_which = OCFS2_AC_USE_MAIN_DISCONTIG;
> bg_bh = ocfs2_block_group_alloc_discontig(handle,
> alloc_inode,
> ac, cl);
> + }
> if (IS_ERR(bg_bh)) {
> status = PTR_ERR(bg_bh);
> bg_bh = NULL;
> @@ -1794,6 +1796,7 @@ static int ocfs2_search_chain(struct ocfs2_alloc_context *ac,
> {
> int status;
> u16 chain;
> + u32 contig_bits;
> u64 next_group;
> struct inode *alloc_inode = ac->ac_inode;
> struct buffer_head *group_bh = NULL;
> @@ -1819,10 +1822,21 @@ static int ocfs2_search_chain(struct ocfs2_alloc_context *ac,
> status = -ENOSPC;
> /* for now, the chain search is a bit simplistic. We just use
> * the 1st group with any empty bits. */
> - while ((status = ac->ac_group_search(alloc_inode, group_bh,
> - bits_wanted, min_bits,
> - ac->ac_max_block,
> - res)) == -ENOSPC) {
> + while (1) {
> + if (ac->ac_which == OCFS2_AC_USE_MAIN_DISCONTIG) {
> + contig_bits = le16_to_cpu(bg->bg_contig_free_bits);
> + if (!contig_bits)
> + contig_bits = ocfs2_find_max_contig_free_bits(bg->bg_bitmap,
> + le16_to_cpu(bg->bg_bits), 0);
> + if (bits_wanted > contig_bits && contig_bits >= min_bits)
> + bits_wanted = contig_bits;
> + }
> +
> + status = ac->ac_group_search(alloc_inode, group_bh,
> + bits_wanted, min_bits,
> + ac->ac_max_block, res);
> + if (status != -ENOSPC)
> + break;
> if (!bg->bg_next_group)
> break;
>
> @@ -1982,6 +1996,7 @@ static int ocfs2_claim_suballoc_bits(struct ocfs2_alloc_context *ac,
> victim = ocfs2_find_victim_chain(cl);
> ac->ac_chain = victim;
>
> +search:
> status = ocfs2_search_chain(ac, handle, bits_wanted, min_bits,
> res, &bits_left);
> if (!status) {
> @@ -2022,6 +2037,16 @@ static int ocfs2_claim_suballoc_bits(struct ocfs2_alloc_context *ac,
> }
> }
>
> + /* Chains can't supply the bits_wanted contiguous space.
> + * We should switch to using every single bit when allocating
> + * from the global bitmap. */
> + if (i == le16_to_cpu(cl->cl_next_free_rec) &&
> + status == -ENOSPC && ac->ac_which == OCFS2_AC_USE_MAIN) {
> + ac->ac_which = OCFS2_AC_USE_MAIN_DISCONTIG;
> + ac->ac_chain = victim;
> + goto search;
> + }
> +
> set_hint:
> if (status != -ENOSPC) {
> /* If the next search of this group is not likely to
> @@ -2365,7 +2390,8 @@ int __ocfs2_claim_clusters(handle_t *handle,
> BUG_ON(ac->ac_bits_given >= ac->ac_bits_wanted);
>
> BUG_ON(ac->ac_which != OCFS2_AC_USE_LOCAL
> - && ac->ac_which != OCFS2_AC_USE_MAIN);
> + && ac->ac_which != OCFS2_AC_USE_MAIN
> + && ac->ac_which != OCFS2_AC_USE_MAIN_DISCONTIG);
>
> if (ac->ac_which == OCFS2_AC_USE_LOCAL) {
> WARN_ON(min_clusters > 1);
> diff --git a/fs/ocfs2/suballoc.h b/fs/ocfs2/suballoc.h
> index b481b834857d..bcf2ed4a8631 100644
> --- a/fs/ocfs2/suballoc.h
> +++ b/fs/ocfs2/suballoc.h
> @@ -29,6 +29,7 @@ struct ocfs2_alloc_context {
> #define OCFS2_AC_USE_MAIN 2
> #define OCFS2_AC_USE_INODE 3
> #define OCFS2_AC_USE_META 4
> +#define OCFS2_AC_USE_MAIN_DISCONTIG 5
> u32 ac_which;
>
> /* these are used by the chain search */
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