linux-kernel - Re: [PATCH v3 2/3] mm: rmap: Fix CONT-PTE/PMD size hugetlb issue when migration

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Date:   Tue, 10 May 2022 16:28:47 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Baolin Wang <baolin.wang@...ux.alibaba.com>,
        mike.kravetz@...cle.com, catalin.marinas@....com, will@...nel.org,
        songmuchun@...edance.com, tsbogend@...ha.franken.de,
        James.Bottomley@...senPartnership.com, deller@....de,
        mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org,
        hca@...ux.ibm.com, gor@...ux.ibm.com, agordeev@...ux.ibm.com,
        borntraeger@...ux.ibm.com, svens@...ux.ibm.com,
        ysato@...rs.osdn.me, dalias@...c.org, davem@...emloft.net,
        arnd@...db.de, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-ia64@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-parisc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v3 2/3] mm: rmap: Fix CONT-PTE/PMD size hugetlb issue
 when migration

On Tue, 10 May 2022 16:17:39 -0700 Andrew Morton <akpm@...ux-foundation.org> wrote:

> > +
> > +static inline pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
> > +					  unsigned long addr, pte_t *ptep)
> > +{
> > +	return ptep_get(ptep);
> > +}
> > +
> > +static inline void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
> > +				   pte_t *ptep, pte_t pte)
> > +{
> > +}
> >  #endif	/* CONFIG_HUGETLB_PAGE */
> >  
> 
> This blows up nommu (arm allnoconfig):
> 
> In file included from fs/io_uring.c:71:
> ./include/linux/hugetlb.h: In function 'huge_ptep_clear_flush':
> ./include/linux/hugetlb.h:1100:16: error: implicit declaration of function 'ptep_get' [-Werror=implicit-function-declaration]
>  1100 |         return ptep_get(ptep);
>       |                ^~~~~~~~
> 
> 
> huge_ptep_clear_flush() is only used in CONFIG_NOMMU=n files, so I simply
> zapped this change.
> 

Well that wasn't a great success.  Doing this instead.  It's pretty
nasty - something nicer would be nicer please.

--- a/include/linux/hugetlb.h~mm-rmap-fix-cont-pte-pmd-size-hugetlb-issue-when-migration-fix
+++ a/include/linux/hugetlb.h
@@ -1094,6 +1094,7 @@ static inline void set_huge_swap_pte_at(
 {
 }
 
+#ifdef CONFIG_MMU
 static inline pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
 					  unsigned long addr, pte_t *ptep)
 {
@@ -1104,6 +1105,7 @@ static inline void set_huge_pte_at(struc
 				   pte_t *ptep, pte_t pte)
 {
 }
+#endif
 #endif	/* CONFIG_HUGETLB_PAGE */
 
 static inline spinlock_t *huge_pte_lock(struct hstate *h,
_