Re: [PATCH RFC v3 11/35] mm: Allow an arch to hook into folio allocation when VMA is known

Anshuman Khandual
2024-01-30T09:55:52Z

On 1/25/24 22:12, Alexandru Elisei wrote:
> arm64 uses VM_HIGH_ARCH_0 and VM_HIGH_ARCH_1 for enabling MTE for a VMA.
> When VM_HIGH_ARCH_0, which arm64 renames to VM_MTE, is set for a VMA, and
> the gfp flag __GFP_ZERO is present, the __GFP_ZEROTAGS gfp flag also gets
> set in vma_alloc_zeroed_movable_folio().
>
> Expand this to be more generic by adding an arch hook that modifes the gfp
> flags for an allocation when the VMA is known.
>
> Note that __GFP_ZEROTAGS is ignored by the page allocator unless __GFP_ZERO
> is also set; from that point of view, the current behaviour is unchanged,
> even though the arm64 flag is set in more places. When arm64 will have
> support to reuse the tag storage for data allocation, the uses of the
> __GFP_ZEROTAGS flag will be expanded to instruct the page allocator to try
> to reserve the corresponding tag storage for the pages being allocated.

Right but how will pushing __GFP_ZEROTAGS addition into gfp_t flags further
down via a new arch call back i.e arch_calc_vma_gfp() while still maintaining
(vma->vm_flags & VM_MTE) conditionality improve the current scenario. Because
the page allocator could have still analyzed alloc flags for __GFP_ZEROTAGS
for any additional stuff.

OR this just adds some new core MM paths to get __GFP_ZEROTAGS which was not
the case earlier via this call back.

>
> The flags returned by arch_calc_vma_gfp() are or'ed with the flags set by
> the caller; this has been done to keep an architecture from modifying the
> flags already set by the core memory management code; this is similar to
> how do_mmap() -> calc_vm_flag_bits() -> arch_calc_vm_flag_bits() has been
> implemented. This can be revisited in the future if there's a need to do
> so.
>
> Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
> ---
> arch/arm64/include/asm/page.h | 5 ++---
> arch/arm64/include/asm/pgtable.h | 3 +++
> arch/arm64/mm/fault.c | 19 ++++++-------------
> include/linux/pgtable.h | 7 +++++++
> mm/mempolicy.c | 1 +
> mm/shmem.c | 5 ++++-
> 6 files changed, 23 insertions(+), 17 deletions(-)
>
> diff --git a/arch/arm64/include/asm/page.h b/arch/arm64/include/asm/page.h
> index 2312e6ee595f..88bab032a493 100644
> --- a/arch/arm64/include/asm/page.h
> +++ b/arch/arm64/include/asm/page.h
> @@ -29,9 +29,8 @@ void copy_user_highpage(struct page *to, struct page *from,
> void copy_highpage(struct page *to, struct page *from);
> #define __HAVE_ARCH_COPY_HIGHPAGE
>
> -struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma,
> - unsigned long vaddr);
> -#define vma_alloc_zeroed_movable_folio vma_alloc_zeroed_movable_folio
> +#define vma_alloc_zeroed_movable_folio(vma, vaddr) \
> + vma_alloc_folio(GFP_HIGHUSER_MOVABLE | __GFP_ZERO, 0, vma, vaddr, false)
>
> void tag_clear_highpage(struct page *to);
> #define __HAVE_ARCH_TAG_CLEAR_HIGHPAGE
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 79ce70fbb751..08f0904dbfc2 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -1071,6 +1071,9 @@ static inline void arch_swap_restore(swp_entry_t entry, struct folio *folio)
>
> #endif /* CONFIG_ARM64_MTE */
>
> +#define __HAVE_ARCH_CALC_VMA_GFP
> +gfp_t arch_calc_vma_gfp(struct vm_area_struct *vma, gfp_t gfp);
> +
> /*
> * On AArch64, the cache coherency is handled via the set_pte_at() function.
> */
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 55f6455a8284..4d3f0a870ad8 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -937,22 +937,15 @@ void do_debug_exception(unsigned long addr_if_watchpoint, unsigned long esr,
> NOKPROBE_SYMBOL(do_debug_exception);
>
> /*
> - * Used during anonymous page fault handling.
> + * If this is called during anonymous page fault handling, and the page is
> + * mapped with PROT_MTE, initialise the tags at the point of tag zeroing as this
> + * is usually faster than separate DC ZVA and STGM.
> */
> -struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma,
> - unsigned long vaddr)
> +gfp_t arch_calc_vma_gfp(struct vm_area_struct *vma, gfp_t gfp)
> {
> - gfp_t flags = GFP_HIGHUSER_MOVABLE | __GFP_ZERO;
> -
> - /*
> - * If the page is mapped with PROT_MTE, initialise the tags at the
> - * point of allocation and page zeroing as this is usually faster than
> - * separate DC ZVA and STGM.
> - */
> if (vma->vm_flags & VM_MTE)
> - flags |= __GFP_ZEROTAGS;
> -
> - return vma_alloc_folio(flags, 0, vma, vaddr, false);
> + return __GFP_ZEROTAGS;
> + return 0;
> }
>
> void tag_clear_highpage(struct page *page)
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index c5ddec6b5305..98f81ca08cbe 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -901,6 +901,13 @@ static inline void arch_do_swap_page(struct mm_struct *mm,
> }
> #endif
>
> +#ifndef __HAVE_ARCH_CALC_VMA_GFP
> +static inline gfp_t arch_calc_vma_gfp(struct vm_area_struct *vma, gfp_t gfp)
> +{
> + return 0;
> +}
> +#endif
> +
> #ifndef __HAVE_ARCH_FREE_PAGES_PREPARE
> static inline void arch_free_pages_prepare(struct page *page, int order) { }
> #endif
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 10a590ee1c89..f7ef52760b32 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -2168,6 +2168,7 @@ struct folio *vma_alloc_folio(gfp_t gfp, int order, struct vm_area_struct *vma,
> pgoff_t ilx;
> struct page *page;
>
> + gfp |= arch_calc_vma_gfp(vma, gfp);
> pol = get_vma_policy(vma, addr, order, &ilx);
> page = alloc_pages_mpol(gfp | __GFP_COMP, order,
> pol, ilx, numa_node_id());
> diff --git a/mm/shmem.c b/mm/shmem.c
> index d7c84ff62186..14427e9982f9 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1585,7 +1585,7 @@ static struct folio *shmem_swapin_cluster(swp_entry_t swap, gfp_t gfp,
> */
> static gfp_t limit_gfp_mask(gfp_t huge_gfp, gfp_t limit_gfp)
> {
> - gfp_t allowflags = __GFP_IO | __GFP_FS | __GFP_RECLAIM;
> + gfp_t allowflags = __GFP_IO | __GFP_FS | __GFP_RECLAIM | __GFP_ZEROTAGS;
> gfp_t denyflags = __GFP_NOWARN | __GFP_NORETRY;
> gfp_t zoneflags = limit_gfp & GFP_ZONEMASK;
> gfp_t result = huge_gfp & ~(allowflags | GFP_ZONEMASK);
> @@ -2038,6 +2038,7 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
> gfp_t huge_gfp;
>
> huge_gfp = vma_thp_gfp_mask(vma);
> + huge_gfp |= arch_calc_vma_gfp(vma, huge_gfp);
> huge_gfp = limit_gfp_mask(huge_gfp, gfp);
> folio = shmem_alloc_and_add_folio(huge_gfp,
> inode, index, fault_mm, true);
> @@ -2214,6 +2215,8 @@ static vm_fault_t shmem_fault(struct vm_fault *vmf)
> vm_fault_t ret = 0;
> int err;
>
> + gfp |= arch_calc_vma_gfp(vmf->vma, gfp);
> +
> /*
> * Trinity finds that probing a hole which tmpfs is punching can
> * prevent the hole-punch from ever completing: noted in i_private.