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SubjectRe: [PATCH 8/8] inode: don't softlockup when evicting inodes
On 04/01/2015 04:05 AM, Jan Kara wrote:
> Sorry for a late reply. I was ill last week...
>

That's ok, I was on vacation for the last two weeks ;).

> On Fri 20-03-15 13:14:16, Josef Bacik wrote:
>> On a box with a lot of ram (148gb) I can make the box softlockup after running
>> an fs_mark job that creates hundreds of millions of empty files. This is
>> because we never generate enough memory pressure to keep the number of inodes on
>> our unused list low, so when we go to unmount we have to evict ~100 million
>> inodes. This makes one processor a very unhappy person, so add a cond_resched()
>> in dispose_list() and cond_resched_lock() in the eviction isolation function to
>> combat this. Thanks,
>>
>> Signed-off-by: Josef Bacik <jbacik@fb.com>
>> ---
>> fs/inode.c | 10 ++++++++++
>> 1 file changed, 10 insertions(+)
>>
>> diff --git a/fs/inode.c b/fs/inode.c
>> index b961e5a..c58dbd3 100644
>> --- a/fs/inode.c
>> +++ b/fs/inode.c
>> @@ -574,6 +574,7 @@ static void dispose_list(struct list_head *head)
>> list_del_init(&inode->i_lru);
>>
>> evict(inode);
>> + cond_resched();
> Fine.
>
>> }
>> }
>>
>> @@ -592,6 +593,7 @@ void evict_inodes(struct super_block *sb)
>> LIST_HEAD(dispose);
>>
>> spin_lock(&sb->s_inode_list_lock);
>> +again:
>> list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
>> if (atomic_read(&inode->i_count))
>> continue;
>> @@ -606,6 +608,14 @@ void evict_inodes(struct super_block *sb)
>> inode_lru_list_del(inode);
>> spin_unlock(&inode->i_lock);
>> list_add(&inode->i_lru, &dispose);
>> +
>> + /*
>> + * We can have a ton of inodes to evict at unmount time given
>> + * enough memory, check to see if we need to go to sleep for a
>> + * bit so we don't livelock.
>> + */
>> + if (cond_resched_lock(&sb->s_inode_list_lock))
>> + goto again;
> Not so fine. How this is ever guaranteed to finish? We don't move inodes
> from the i_sb_list in this loop so if we ever take 'goto again' we just
> start doing all the work from the beginning...
>
> What needs to happen is that if we need to resched, we drop
> sb->s_inode_list_lock, call dispose_list(&dispose) and *then* restart from
> the beginning since we have freed all the inodes that we isolated...
>

Ooops, good point. I'll get this fixed up, thanks,

Josef


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