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Message-ID: <spkiynphi76p7bybswvxypro6pkbm7h4jtt2niwg6laqhrwamx@bojwcg3wkviq>
Date: Thu, 5 Sep 2024 11:20:42 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Dev Jain <dev.jain@....com>
Cc: akpm@...ux-foundation.org, david@...hat.com, willy@...radead.org,
ryan.roberts@....com, anshuman.khandual@....com, catalin.marinas@....com,
cl@...two.org, vbabka@...e.cz, mhocko@...e.com, apopple@...dia.com,
dave.hansen@...ux.intel.com, will@...nel.org, baohua@...nel.org, jack@...e.cz,
mark.rutland@....com, hughd@...gle.com, aneesh.kumar@...nel.org,
yang@...amperecomputing.com, peterx@...hat.com, ioworker0@...il.com, jglisse@...gle.com,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 1/2] mm: Abstract THP allocation
On Wed, Sep 04, 2024 at 03:39:22PM +0530, Dev Jain wrote:
> In preparation for the second patch, abstract away the THP allocation
> logic present in the create_huge_pmd() path, which corresponds to the
> faulting case when no page is present.
>
> There should be no functional change as a result of applying
> this patch.
>
> Signed-off-by: Dev Jain <dev.jain@....com>
> ---
> mm/huge_memory.c | 110 +++++++++++++++++++++++++++++------------------
> 1 file changed, 67 insertions(+), 43 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 67c86a5d64a6..58125fbcc532 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -943,47 +943,89 @@ unsigned long thp_get_unmapped_area(struct file *filp, unsigned long addr,
> }
> EXPORT_SYMBOL_GPL(thp_get_unmapped_area);
>
> -static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
> - struct page *page, gfp_t gfp)
> +static vm_fault_t thp_fault_alloc(gfp_t gfp, int order, struct vm_area_struct *vma,
> + unsigned long haddr, struct folio **foliop,
> + unsigned long addr)
foliop is awkward.
Why not return folio? NULL would indicate to the caller to fallback.
> {
> - struct vm_area_struct *vma = vmf->vma;
> - struct folio *folio = page_folio(page);
> - pgtable_t pgtable;
> - unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
> - vm_fault_t ret = 0;
> + struct folio *folio = vma_alloc_folio(gfp, order, vma, haddr, true);
>
> - VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
> + *foliop = folio;
> + if (unlikely(!folio)) {
> + count_vm_event(THP_FAULT_FALLBACK);
> + count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK);
> + return VM_FAULT_FALLBACK;
> + }
>
> + VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
> if (mem_cgroup_charge(folio, vma->vm_mm, gfp)) {
> folio_put(folio);
> count_vm_event(THP_FAULT_FALLBACK);
> count_vm_event(THP_FAULT_FALLBACK_CHARGE);
> - count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_FALLBACK);
> - count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
> + count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK);
> + count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
> return VM_FAULT_FALLBACK;
> }
> folio_throttle_swaprate(folio, gfp);
>
> - pgtable = pte_alloc_one(vma->vm_mm);
> - if (unlikely(!pgtable)) {
> - ret = VM_FAULT_OOM;
> - goto release;
> - }
> -
> - folio_zero_user(folio, vmf->address);
> + folio_zero_user(folio, addr);
> /*
> * The memory barrier inside __folio_mark_uptodate makes sure that
> * folio_zero_user writes become visible before the set_pmd_at()
> * write.
> */
> __folio_mark_uptodate(folio);
> + return 0;
> +}
> +
> +static void __thp_fault_success_stats(struct vm_area_struct *vma, int order)
> +{
> + count_vm_event(THP_FAULT_ALLOC);
> + count_mthp_stat(order, MTHP_STAT_ANON_FAULT_ALLOC);
> + count_memcg_event_mm(vma->vm_mm, THP_FAULT_ALLOC);
> +}
> +
> +static void map_pmd_thp(struct folio *folio, struct vm_fault *vmf,
> + struct vm_area_struct *vma, unsigned long haddr,
> + pgtable_t pgtable)
> +{
> + pmd_t entry;
> +
> + entry = mk_huge_pmd(&folio->page, vma->vm_page_prot);
> + entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
> + folio_add_new_anon_rmap(folio, vma, haddr, RMAP_EXCLUSIVE);
> + folio_add_lru_vma(folio, vma);
> + pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
> + set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
> + update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
> + add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
> + mm_inc_nr_ptes(vma->vm_mm);
> +}
> +
> +static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf)
> +{
> + struct vm_area_struct *vma = vmf->vma;
> + struct folio *folio = NULL;
> + pgtable_t pgtable;
> + unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
> + vm_fault_t ret = 0;
> + gfp_t gfp = vma_thp_gfp_mask(vma);
> +
> + pgtable = pte_alloc_one(vma->vm_mm);
> + if (unlikely(!pgtable)) {
> + ret = VM_FAULT_OOM;
> + goto release;
> + }
> +
> + ret = thp_fault_alloc(gfp, HPAGE_PMD_ORDER, vma, haddr, &folio,
> + vmf->address);
> + if (ret)
> + goto release;
THP page allocation has higher probability to fail than pgtable allocation. It
is better to allocate it first, before pgtable and do less work on error
path.
> vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
> +
> if (unlikely(!pmd_none(*vmf->pmd))) {
> goto unlock_release;
> } else {
> - pmd_t entry;
> -
> ret = check_stable_address_space(vma->vm_mm);
> if (ret)
> goto unlock_release;
> @@ -997,20 +1039,9 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
> VM_BUG_ON(ret & VM_FAULT_FALLBACK);
> return ret;
> }
> -
> - entry = mk_huge_pmd(page, vma->vm_page_prot);
> - entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
> - folio_add_new_anon_rmap(folio, vma, haddr, RMAP_EXCLUSIVE);
> - folio_add_lru_vma(folio, vma);
> - pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
> - set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
> - update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
> - add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
> - mm_inc_nr_ptes(vma->vm_mm);
> + map_pmd_thp(folio, vmf, vma, haddr, pgtable);
> spin_unlock(vmf->ptl);
> - count_vm_event(THP_FAULT_ALLOC);
> - count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_ALLOC);
> - count_memcg_event_mm(vma->vm_mm, THP_FAULT_ALLOC);
> + __thp_fault_success_stats(vma, HPAGE_PMD_ORDER);
> }
>
> return 0;
> @@ -1019,7 +1050,8 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
> release:
> if (pgtable)
> pte_free(vma->vm_mm, pgtable);
> - folio_put(folio);
> + if (folio)
> + folio_put(folio);
> return ret;
>
> }
> @@ -1077,8 +1109,6 @@ static void set_huge_zero_folio(pgtable_t pgtable, struct mm_struct *mm,
> vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf)
> {
> struct vm_area_struct *vma = vmf->vma;
> - gfp_t gfp;
> - struct folio *folio;
> unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
> vm_fault_t ret;
>
> @@ -1129,14 +1159,8 @@ vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf)
> }
> return ret;
> }
> - gfp = vma_thp_gfp_mask(vma);
> - folio = vma_alloc_folio(gfp, HPAGE_PMD_ORDER, vma, haddr, true);
> - if (unlikely(!folio)) {
> - count_vm_event(THP_FAULT_FALLBACK);
> - count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_FALLBACK);
> - return VM_FAULT_FALLBACK;
> - }
> - return __do_huge_pmd_anonymous_page(vmf, &folio->page, gfp);
> +
> + return __do_huge_pmd_anonymous_page(vmf);
> }
>
> static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
> --
> 2.30.2
>
--
Kiryl Shutsemau / Kirill A. Shutemov
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