Re: [PATCH v2] tmpfs: fault in smaller chunks if large folio allocation not allowed

[Kefeng Wang <wangkefeng.wang@huawei.com>]

On 2024/9/30 10:02, Baolin Wang wrote:
> 
> 
> On 2024/9/26 21:52, Matthew Wilcox wrote:
>> On Thu, Sep 26, 2024 at 10:38:34AM +0200, Pankaj Raghav (Samsung) wrote:
>>>> So this is why I don't use mapping_set_folio_order_range() here, but
>>>> correct me if I am wrong.
>>>
>>> Yeah, the inode is active here as the max folio size is decided based on
>>> the write size, so probably mapping_set_folio_order_range() will not be
>>> a safe option.
>>
>> You really are all making too much of this.  Here's the patch I think we
>> need:
>>
>> +++ b/mm/shmem.c
>> @@ -2831,7 +2831,8 @@ static struct inode *__shmem_get_inode(struct 
>> mnt_idmap *idmap,
>>          cache_no_acl(inode);
>>          if (sbinfo->noswap)
>>                  mapping_set_unevictable(inode->i_mapping);
>> -       mapping_set_large_folios(inode->i_mapping);
>> +       if (sbinfo->huge)
>> +               mapping_set_large_folios(inode->i_mapping);
>>
>>          switch (mode & S_IFMT) {
>>          default:
> 
> IMHO, we no longer need the the 'sbinfo->huge' validation after adding 
> support for large folios in the tmpfs write and fallocate paths [1].
> 
> Kefeng, can you try if the following RFC patch [1] can solve your 
> problem? Thanks.
> (PS: I will revise the patch according to Matthew's suggestion)

Sure, will try once I come back, but [1] won't solve the issue when set
force/deny at runtime, eg, mount with always/within_size, but set deny 
when runtime, we still fault in large chunks, but we can't allocate 
large folio, the performance of write will be degradation.


> 
> [1] https://lore.kernel.org/all/ 
> c03ec1cb1392332726ab265a3d826fe1c408c7e7.1727338549.git.baolin.wang@linux.alibaba.com/