Re: [PATCHv9-rebased2 11/37] mm: introduce do_set_pmd()

["Hillf Danton" <hillf.zj@alibaba-inc.com>]

> +
> +static int do_set_pmd(struct fault_env *fe, struct page *page)
> +{
> +	struct vm_area_struct *vma = fe->vma;
> +	bool write = fe->flags & FAULT_FLAG_WRITE;
> +	unsigned long haddr = fe->address & HPAGE_PMD_MASK;
> +	pmd_t entry;
> +	int i, ret;
> +
> +	if (!transhuge_vma_suitable(vma, haddr))
> +		return VM_FAULT_FALLBACK;
> +
> +	ret = VM_FAULT_FALLBACK;
> +	page = compound_head(page);
> +
> +	fe->ptl = pmd_lock(vma->vm_mm, fe->pmd);
> +	if (unlikely(!pmd_none(*fe->pmd)))
> +		goto out;

Can we reply to the caller that fault is handled correctly(by
resetting ret to zero before jump)?

> +
> +	for (i = 0; i < HPAGE_PMD_NR; i++)
> +		flush_icache_page(vma, page + i);
> +
> +	entry = mk_huge_pmd(page, vma->vm_page_prot);
> +	if (write)
> +		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
> +
> +	add_mm_counter(vma->vm_mm, MM_FILEPAGES, HPAGE_PMD_NR);
> +	page_add_file_rmap(page, true);
> +
> +	set_pmd_at(vma->vm_mm, haddr, fe->pmd, entry);
> +
> +	update_mmu_cache_pmd(vma, haddr, fe->pmd);
> +
> +	/* fault is handled */
> +	ret = 0;
> +out:
> +	spin_unlock(fe->ptl);
> +	return ret;
> +}
> +#else
> +static int do_set_pmd(struct fault_env *fe, struct page *page)
> +{
> +	BUILD_BUG();
> +	return 0;
> +}
> +#endif
> +
>  /**
>   * alloc_set_pte - setup new PTE entry for given page and add reverse page
>   * mapping. If needed, the fucntion allocates page table or use pre-allocated.
> @@ -2940,9 +3000,19 @@ int alloc_set_pte(struct fault_env *fe, struct mem_cgroup *memcg,
>  	struct vm_area_struct *vma = fe->vma;
>  	bool write = fe->flags & FAULT_FLAG_WRITE;
>  	pte_t entry;
> +	int ret;
> +
> +	if (pmd_none(*fe->pmd) && PageTransCompound(page)) {
> +		/* THP on COW? */
> +		VM_BUG_ON_PAGE(memcg, page);
> +
> +		ret = do_set_pmd(fe, page);
> +		if (ret != VM_FAULT_FALLBACK)
> +			return ret;
> +	}
> 
>  	if (!fe->pte) {
> -		int ret = pte_alloc_one_map(fe);
> +		ret = pte_alloc_one_map(fe);
>  		if (ret)
>  			return ret;
>  	}
> diff --git a/mm/migrate.c b/mm/migrate.c

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