linux-kernel - Re: [PATCH] ocfs2: fixing global bitmap allocating failure for discontig type

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Message-ID: <590fe587-0df7-4aa4-a8c0-b9120d658f6f@suse.com>
Date: Tue, 1 Apr 2025 21:50:10 +0800
From: Heming Zhao <heming.zhao@...e.com>
To: Joseph Qi <joseph.qi@...ux.alibaba.com>
Cc: ocfs2-devel@...ts.linux.dev, linux-kernel@...r.kernel.org,
 gautham.ananthakrishna@...cle.com
Subject: Re: [PATCH] ocfs2: fixing global bitmap allocating failure for
 discontig type

On 4/1/25 19:38, Joseph Qi wrote:
> 
> 
> On 2025/3/27 14:22, Heming Zhao wrote:
>> The commit 4eb7b93e0310 ("ocfs2: improve write IO performance when
>> fragmentation is high") introduced a regression. In the discontiguous
>> extent allocation case, ocfs2_cluster_group_search() is comparing with
>> the wrong target length, which causes allocation failure.
>>
>> Call stack:
>> ocfs2_mkdir()
>>   ocfs2_reserve_new_inode()
>>    ocfs2_reserve_suballoc_bits()
>>     ocfs2_block_group_alloc()
>>      ocfs2_block_group_alloc_discontig()
>>       __ocfs2_claim_clusters()
>>        ocfs2_claim_suballoc_bits()
>>         ocfs2_search_chain()
>>          ocfs2_cluster_group_search()
>>
>> Reported-by: Gautham Ananthakrishna <gautham.ananthakrishna@...cle.com>
>> Fixes: 4eb7b93e0310 ("ocfs2: improve write IO performance when fragmentation is high")
>> Signed-off-by: Heming Zhao <heming.zhao@...e.com>
>> ---
>>   fs/ocfs2/suballoc.c | 14 +++++++++++---
>>   fs/ocfs2/suballoc.h |  1 +
>>   2 files changed, 12 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c
>> index f7b483f0de2a..3dea082f6e91 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;
>> @@ -2365,7 +2367,8 @@ 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);
>> @@ -2427,7 +2430,12 @@ int ocfs2_claim_clusters(handle_t *handle,
>>   			 u32 *cluster_start,
>>   			 u32 *num_clusters)
>>   {
>> -	unsigned int bits_wanted = ac->ac_bits_wanted - ac->ac_bits_given;
>> +	unsigned int bits_wanted;
>> +
>> +	if (ac->ac_which == OCFS2_AC_USE_MAIN)
>> +		bits_wanted = ac->ac_bits_wanted - ac->ac_bits_given;
>> +	else /* ac_which == OCFS2_AC_USE_MAIN_DISCONTIG */
>> +		bits_wanted = min_clusters;
> 
> This looks wried. Why can not be other alloc type?
> 
> Or it seems you intend to:
> 
> unsigned int bits_wanted = ac->ac_bits_wanted - ac->ac_bits_given;
> 
> if (ac->ac_which == OCFS2_AC_USE_MAIN_DISCONTIG)
> 	bits_wanted = min_clusters;
> 
> Thanks,
> Joseph

Yes, you are right.
We should use OCFS2_AC_USE_MAIN_DISCONTIG to handle the special discontig case.
Will send v2 patch for this mistake.

- Heming
> 
>>   
>>   	return __ocfs2_claim_clusters(handle, ac, min_clusters,
>>   				      bits_wanted, cluster_start, num_clusters);
>> 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 */
>