[PATCH 00/15] ubifs folio conversion

[Zhihao Cheng]

在 2024/1/24 13:01, Matthew Wilcox 写道:
> On Tue, Jan 23, 2024 at 08:33:49AM +0100, Richard Weinberger wrote:
>> Matthew,
>>
>> ----- Ursprüngliche Mail -----
>>> Von: "Matthew Wilcox" <willy at infradead.org>
>>> An: "richard" <richard at nod.at>
>>> CC: "Matthew Wilcox" <willy at infradead.org>, "linux-mtd" <linux-mtd at lists.infradead.org>
>>> Gesendet: Sonntag, 21. Januar 2024 00:08:08
>>> Betreff: [PATCH 00/15] ubifs folio conversion
>>
>>> This patchset converts ubifs to use folios throughout.  I made some
>>> attempt to support large folios, but more work definitely needs to be
>>> done before it can be enabled.  It's not clear to me whether it's worth
>>> doing, so I've left that for you ;-)
>>
>> what is the benefit of large folios?
> 
> For another purpose, I just wrote this up.  Possibly there are more
> benefits, but these are the ones I remembered just now:
> 
> But why should a filesystem put in the effort to support large folios
> (aka multi-page folios)?
> 
>      Lower overheads
>          Fewer calls to the page allocator
>          Shorter LRU list helps vmscan age memory
>          Fewer calls to the page cache for large read()/write()
>          Fewer calls to the architecture code for handling faults in mmaped files
>          Potential use of larger TLB entries (eg contPTE / NAPOT)
>      Being a better kernel citizen
>          The more code using large folios, the easier it is to allocate large folios
> 
> The costs may outweigh the benefits. I would not invest time in making
> iso9660, adfs or efs support large folios. But for filesystems which
> are used every day (XFS, NFS, ext4, btrfs, ...) the benefit is very much
> worth the cost.

Ext4 could gain a good performance based on large folio[1], one 
important reason is that blocks allocation method is changed as batch 
allocation from one by one. There is a difference between UBIFS and ext4 
on IO logic, so I'm not sure how much performance the large folio will 
bring to UBIFS. I think page will be replaced by folio some day, so 
these patches can be a folio switching and a preparation for large folio 
support on UBIFS, personally I think.

[1] https://lwn.net/Articles/956575/