Re: [PATCH v3 0/5] add persistent huge zero folio support

[IBM]

"Pankaj Raghav (Samsung)" <kernel@xxxxxxxxxxxxxxxx> writes:

>> > > > Add a config option PERSISTENT_HUGE_ZERO_FOLIO that will always allocate
>> > > > the huge_zero_folio, and disable the shrinker so that huge_zero_folio is
>> > > > never freed.
>> > > > This makes using the huge_zero_folio without having to pass any mm struct and does
>> > > > not tie the lifetime of the zero folio to anything, making it a drop-in
>> > > > replacement for ZERO_PAGE.
>> > > > 
>> > > > I have converted blkdev_issue_zero_pages() as an example as a part of
>> > > > this series. I also noticed close to 4% performance improvement just by
>> > > > replacing ZERO_PAGE with persistent huge_zero_folio.
>> > > > 
>> > > > I will send patches to individual subsystems using the huge_zero_folio
>> > > > once this gets upstreamed.
>> > > > 
>> > > > Looking forward to some feedback.
>> > > 
>> > > Why does it need to be compile-time? Maybe whoever needs huge zero page
>> > > would just call get_huge_zero_page()/folio() on initialization to get it
>> > > pinned?
>> > 
>> > That's what v2 did, and this way here is cleaner.
>> 
>> Sorry, RFC v2 I think. It got a bit confusing with series names/versions.
>> 
>
> Another reason we made it a compile time config is because not all
> machines would want a PMD sized folio just for zeroing. For example,
> Dave Hansen told in one of the early revisions that a small x86 VM would
> not want this.
>
> So it is a default N, and it will be an opt-in.
>

I looked over the patches and I liked this design. This is much simpler
and cleaner compared to the initial version. 

Thanks!
-ritesh