linux-kernel - Re: [PATCH v6 16/26] huge_memory: Add vmf_insert_folio

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Message-ID: <31919e6c-0cec-4e3a-a0c6-a80be53d6ccc@redhat.com>
Date: Tue, 14 Jan 2025 17:40:35 +0100
From: David Hildenbrand <david@...hat.com>
To: Alistair Popple <apopple@...dia.com>, akpm@...ux-foundation.org,
 dan.j.williams@...el.com, linux-mm@...ck.org
Cc: alison.schofield@...el.com, lina@...hilina.net, zhang.lyra@...il.com,
 gerald.schaefer@...ux.ibm.com, vishal.l.verma@...el.com,
 dave.jiang@...el.com, logang@...tatee.com, bhelgaas@...gle.com,
 jack@...e.cz, jgg@...pe.ca, catalin.marinas@....com, will@...nel.org,
 mpe@...erman.id.au, npiggin@...il.com, dave.hansen@...ux.intel.com,
 ira.weiny@...el.com, willy@...radead.org, djwong@...nel.org, tytso@....edu,
 linmiaohe@...wei.com, peterx@...hat.com, linux-doc@...r.kernel.org,
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 linuxppc-dev@...ts.ozlabs.org, nvdimm@...ts.linux.dev,
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Subject: Re: [PATCH v6 16/26] huge_memory: Add vmf_insert_folio_pmd()

> +vm_fault_t vmf_insert_folio_pmd(struct vm_fault *vmf, struct folio *folio, bool write)
> +{
> +	struct vm_area_struct *vma = vmf->vma;
> +	unsigned long addr = vmf->address & PMD_MASK;
> +	struct mm_struct *mm = vma->vm_mm;
> +	spinlock_t *ptl;
> +	pgtable_t pgtable = NULL;
> +
> +	if (addr < vma->vm_start || addr >= vma->vm_end)
> +		return VM_FAULT_SIGBUS;
> +
> +	if (WARN_ON_ONCE(folio_order(folio) != PMD_ORDER))
> +		return VM_FAULT_SIGBUS;
> +
> +	if (arch_needs_pgtable_deposit()) {
> +		pgtable = pte_alloc_one(vma->vm_mm);
> +		if (!pgtable)
> +			return VM_FAULT_OOM;
> +	}

This is interesting and nasty at the same time (only to make ppc64 boo3s 
with has tables happy). But it seems to be the right thing to do.

> +
> +	ptl = pmd_lock(mm, vmf->pmd);
> +	if (pmd_none(*vmf->pmd)) {
> +		folio_get(folio);
> +		folio_add_file_rmap_pmd(folio, &folio->page, vma);
> +		add_mm_counter(mm, mm_counter_file(folio), HPAGE_PMD_NR);
> +	}
> +	insert_pfn_pmd(vma, addr, vmf->pmd, pfn_to_pfn_t(folio_pfn(folio)),
> +		       vma->vm_page_prot, write, pgtable);
> +	spin_unlock(ptl);
> +	if (pgtable)
> +		pte_free(mm, pgtable);

Ehm, are you unconditionally freeing the pgtable, even if consumed by 
insert_pfn_pmd() ?

Note that setting pgtable to NULL in insert_pfn_pmd() when consumed will 
not be visible here.

You'd have to pass a pointer to the ... pointer (&pgtable).

... unless I am missing something, staring at the diff.

-- 
Cheers,

David / dhildenb