linux-kernel - Re: [PATCH v3 3/4] mm/hugetlb: Refactor __unmap_hugepage

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Message-ID: <aBfdls-Sw4VpMWQY@lg>
Date: Sun, 4 May 2025 14:35:18 -0700
From: Fan Ni <nifan.cxl@...il.com>
To: Oscar Salvador <osalvador@...e.de>
Cc: nifan.cxl@...il.com, muchun.song@...ux.dev, willy@...radead.org,
	mcgrof@...nel.org, a.manzanares@...sung.com, dave@...olabs.net,
	akpm@...ux-foundation.org, david@...hat.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/4] mm/hugetlb: Refactor __unmap_hugepage_range() to
 take folio instead of page

On Wed, Apr 30, 2025 at 09:58:35AM +0200, Oscar Salvador wrote:
> On Mon, Apr 28, 2025 at 10:11:46AM -0700, nifan.cxl@...il.com wrote:
> > From: Fan Ni <fan.ni@...sung.com>
> > 
> > The function __unmap_hugepage_range() has two kinds of users:
> > 1) unmap_hugepage_range(), which passes in the head page of a folio.
> >    Since unmap_hugepage_range() already takes folio and there are no other
> >    uses of the folio struct in the function, it is natural for
> >    __unmap_hugepage_range() to take folio also.
> > 2) All other uses, which pass in NULL pointer.
> > 
> > In both cases, we can pass in folio. Refactor __unmap_hugepage_range() to
> > take folio.
> > 
> > Signed-off-by: Fan Ni <fan.ni@...sung.com>
> 
> Reviewed-by: Oscar Salvador <osalvador@...e.de>
> 
> But:
> 
> >  void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
> >  			    unsigned long start, unsigned long end,
> > -			    struct page *ref_page, zap_flags_t zap_flags)
> > +			    struct folio *folio, zap_flags_t zap_flags)
> 
> I think we are kinda losing information here. ref_ was a good hint
> and...

Hi Oscar,

Thanks for the feedback.
Since the sugguested change here is minor and does not affect the
function, and we do not have a aligned opinion here.
https://lore.kernel.org/linux-mm/b23ef51b-1284-4168-8157-432c3e045788@redhat.com/
I will leave it as it is until there are more pushes for the change.


> 
> >  	struct mm_struct *mm = vma->vm_mm;
> >  	unsigned long address;
> > @@ -5885,8 +5885,8 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
> >  		 * page is being unmapped, not a range. Ensure the page we
> >  		 * are about to unmap is the actual page of interest.
> >  		 */
> > -		if (ref_page) {
> > -			if (page != ref_page) {
> > +		if (folio) {
> > +			if (page_folio(page) != folio) {
> 
> You have to update the comment above, since we are not passing a
> reference page anymore but a folio.

Will update in the next version. Thanks.

Fan

> 
>  
> 
> -- 
> Oscar Salvador
> SUSE Labs
> 

-- 
Fan Ni