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

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

On 2024/9/22 8:35, Matthew Wilcox wrote:
> On Fri, Sep 20, 2024 at 10:36:54PM +0800, Kefeng Wang wrote:
>> The tmpfs supports large folio, but there is some configurable options
>> to enable/disable large folio allocation, and for huge=within_size,
>> large folio only allowabled if it fully within i_size, so there is
>> performance issue when perform write without large folio, the issue is
>> similar to commit 4e527d5841e2 ("iomap: fault in smaller chunks for
>> non-large folio mappings").
> 
> No.  What's wrong with my earlier suggestion?
> 

The tempfs has mount options(never/always/within_size/madvise) for large
folio, also has sysfs file /sys/kernel/mm/transparent_hugepage/shmem_enabled
to deny/force large folio at runtime, as replied in v1, I think it
breaks the rules of mapping_set_folio_order_range(),

   "Do not tune it based on, eg, i_size."
   --- for tmpfs, it does choose large folio or not based on the i_size

   "Context: This should not be called while the inode is active as it 
is non-atomic."
   --- during perform write, the inode is active

So this is why I don't use mapping_set_folio_order_range() here, but
correct me if I am wrong.