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Message-ID: <10aea3c3-42be-4f82-8961-75d5142a9653@arm.com>
Date: Fri, 6 Sep 2024 11:12:10 +0530
From: Dev Jain <dev.jain@....com>
To: Ryan Roberts <ryan.roberts@....com>, akpm@...ux-foundation.org,
david@...hat.com, willy@...radead.org, kirill.shutemov@...ux.intel.com
Cc: 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 9/5/24 16:38, Ryan Roberts wrote:
> On 04/09/2024 11:09, 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,
> Is there a reason for specifying order as a parameter? Previously it was
> hardcoded to HPAGE_PMD_ORDER. But now, thp_fault_alloc() and
> __thp_fault_success_stats() both take order and map_pmd_thp() is still
> implicitly mapping a PMD-sized block. Unless there is a reason you need this
> parameter in the next patch (I don't think there is?) I suggest simplifying.
If I am not wrong, thp_fault_alloc() and __thp_fault_success_stats()
will remain the same in case of mTHP? I chose to pass order so that these
functions can be used by others in the future. Therefore, these two functions
can be generically used in the future while map_pmd_thp() (as the name suggests)
maps only a PMD-mappable THP.
>
>> + unsigned long haddr, struct folio **foliop,
> FWIW, I agree with Kirill's suggestion to just return folio* and drop the output
> param.
As I replied to Kirill, I do not think that is a good idea. If you do a git grep on
the tree for "foliop", you will find several places where that is being used, for
example, check out alloc_charge_folio() in mm/khugepaged.c. The author intends to
do the stat computation and setting *foliop in the function itself, so that the
caller is only concerned with the return value.
Also, if we return the folio instead of VM_FAULT_FALLBACK from thp_fault_alloc(),
then you will have two "if (unlikely(!folio))" branches, the first to do the stat
computation in the function, and the second branch in the caller to set ret = VM_FAULT_FALLBACK
and then goto out/release.
And, it is already inconsistent to break away the stat computation and the return value
setting, when the stat computation name is of the form "count_vm_event(THP_FAULT_FALLBACK)"
and friends, at which point it would just be better to open code the function.
If I am missing something and your suggestion can be implemented neatly, please guide.
>
> Thanks,
> Ryan
>
>> + 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;
>> + 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;
>>
>> 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,
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