Re: [PATCH resend 1/2] mm: always use base address when clear gigantic page

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

On 2024/10/26 6:56, Andrew Morton wrote:
> On Fri, 25 Oct 2024 08:44:55 +0800 Kefeng Wang <wangkefeng.wang@huawei.com> wrote:
> 
>> When clear gigantic page, it zeros page from the first subpage to
>> the last subpage, that is, aligned base address is needed in it,
>> and we don't need to aligned down the address in the caller as the
>> real address will be passed to process_huge_page().
> 
> Matthew just told us that folios con't have subpages
> (https://lkml.kernel.org/r/ZxsRCyBSO-C27Uzn@casper.infradead.org).
> 

OK, will change subpage to page.

> Please carefully describe the impact of this change.  I think it's
> "small cleanup and optimization?"
> 
> Also, I find the changelog rather hard to follow.  I think we're adding
> the alignment operation to the callee and hence removing it from the
> caller?
> 

Sorry for the confuse, there is some different between gigantic
page(nr_pages > MAX_ORDER_NR_PAGE) and non-gigantic page,

1) for gigantic page, it always clear/copy page from the fist page to
the last page, see copy_user_gigantic_page/clear_gigantic_page, but if 
directly pass addr_hint which maybe not the address of the first page,
then if arch's code use this addr_hint to flush cache, it may flush the 
wrong cache.

2) for non-gigantic page, it calculate the base address inside, see 
process_huge_page, if we passed the wrong addr_hint, it only has 
performance impact(not sure, but at least no different on arm64), no
function impact.

Will update the change and resend.