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Message-ID: <2200396e-9f70-41ac-b8cb-c207501a7770@arm.com>
Date: Tue, 24 Sep 2024 09:55:24 +0530
From: Dev Jain <dev.jain@....com>
To: David Hildenbrand <david@...hat.com>, akpm@...ux-foundation.org,
willy@...radead.org, kirill.shutemov@...ux.intel.com
Cc: 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, wangkefeng.wang@...wei.com,
ziy@...dia.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v4 1/2] mm: Abstract THP allocation
On 9/17/24 17:17, David Hildenbrand wrote:
> On 16.09.24 11:43, 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,
>> except that, as David notes at [1], a PMD-aligned address should
>> be passed to update_mmu_cache_pmd().
>>
>> [1]:
>> https://lore.kernel.org/all/ddd3fcd2-48b3-4170-bcaa-2fe66e093f43@redhat.com/
>>
>> Signed-off-by: Dev Jain <dev.jain@....com>
>> ---
>> mm/huge_memory.c | 108 +++++++++++++++++++++++++++++------------------
>> 1 file changed, 66 insertions(+), 42 deletions(-)
>>
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index 2a73efea02d7..cdc632b8dc9c 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -1146,47 +1146,88 @@ 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 struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct
>> *vma,
>> + unsigned long addr)
>> {
>> - 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;
>> + unsigned long haddr = addr & HPAGE_PMD_MASK;
>> + gfp_t gfp = vma_thp_gfp_mask(vma);
>> + const int order = HPAGE_PMD_ORDER;
>> + struct folio *folio = vma_alloc_folio(gfp, order, vma, haddr,
>> true);
>> - VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
>> + if (unlikely(!folio)) {
>> + count_vm_event(THP_FAULT_FALLBACK);
>> + count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK);
>> + goto out;
>> + }
>> + 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);
>> - return VM_FAULT_FALLBACK;
>> + count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK);
>> + count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
>> + return NULL;
>> }
>> 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);
>> +out:
>> + return folio;
>> +}
>> +
>> +static void __pmd_thp_fault_success_stats(struct vm_area_struct *vma)
>> +{
>> + 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);
>> +}
>
> just inline that into map_anon_folio_pmd(), please. map_anon_folio_pmd
> is perfectly readable ;)
If you are asking me to open code it in map_anon_folio_pmd(), I'll do that.
>
>> +
>> +static void map_anon_folio_pmd(struct folio *folio, pmd_t *pmd,
>> + struct vm_area_struct *vma, unsigned long haddr)
>
>
>> +{
>> + 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);
>> + set_pmd_at(vma->vm_mm, haddr, pmd, entry);
>> + update_mmu_cache_pmd(vma, haddr, pmd);
>> + add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
>> + __pmd_thp_fault_success_stats(vma);
>> +}
>> +
>> +static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf)
>> +{
>> + unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
>> + struct vm_area_struct *vma = vmf->vma;
>> + pgtable_t pgtable = NULL;
>> + struct folio *folio;
>> + vm_fault_t ret = 0;
>> +
>> + folio = vma_alloc_anon_folio_pmd(vma, vmf->address);
>> + if (unlikely(!folio)) {
>> + ret = VM_FAULT_FALLBACK;
>> + goto release;
>
> Why not simply "return VM_FAULT_FALLBACK;" ? There is nothing to
> release. Then you can avoid the
>
> "if (folio)" below and even stop initializing pgtable to NULL.
Makes sense.
>
>
> With these things take care of
>
> Acked-by: David Hildenbrand <david@...hat.com>
Thanks!
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