Re: [PATCH v3 1/2] mm: Abstract THP allocation

[Dev Jain]

On 9/11/24 16:22, Kefeng Wang wrote:
> On 2024/9/11 14:55, 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@xxxxxxx>
> > ---
> >   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..b96a1ff2bf40 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -943,47 +943,88 @@ 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 *pmd_thp_fault_alloc(gfp_t gfp, struct 
> > vm_area_struct *vma,
> > +                     unsigned long haddr, 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;
> > +    const int order = HPAGE_PMD_ORDER;
>
> Maybe move vma_thp_gfp_mask() into this function too.

That's better, thanks.
> > +    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);
> > +        goto out;
>
> We need to return NULL here as folio not set to null,

My bad for assuming that folio_put() also sets folio to NULL. I read
through the code path for that and I guess it does not. Thanks.
> >       }
> >       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;
> > +}
> > +