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Message-ID: <CAOUHufYef--8MxFettL6fOGjVx2vyZHZQU6EEaTCoW0XBvuC8Q@mail.gmail.com>
Date: Wed, 12 Jul 2023 00:31:54 -0600
From: Yu Zhao <yuzhao@...gle.com>
To: Yin Fengwei <fengwei.yin@...el.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
akpm@...ux-foundation.org, willy@...radead.org, david@...hat.com,
ryan.roberts@....com, shy828301@...il.com
Subject: Re: [RFC PATCH v2 3/3] mm: mlock: update mlock_pte_range to handle
large folio
On Wed, Jul 12, 2023 at 12:02 AM Yin Fengwei <fengwei.yin@...el.com> wrote:
>
> Current kernel only lock base size folio during mlock syscall.
> Add large folio support with following rules:
> - Only mlock large folio when it's in VM_LOCKED VMA range
>
> - If there is cow folio, mlock the cow folio as cow folio
> is also in VM_LOCKED VMA range.
>
> - munlock will apply to the large folio which is in VMA range
> or cross the VMA boundary.
>
> The last rule is used to handle the case that the large folio is
> mlocked, later the VMA is split in the middle of large folio
> and this large folio become cross VMA boundary.
>
> Signed-off-by: Yin Fengwei <fengwei.yin@...el.com>
> ---
> mm/mlock.c | 104 ++++++++++++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 99 insertions(+), 5 deletions(-)
>
> diff --git a/mm/mlock.c b/mm/mlock.c
> index 0a0c996c5c214..f49e079066870 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -305,6 +305,95 @@ void munlock_folio(struct folio *folio)
> local_unlock(&mlock_fbatch.lock);
> }
>
> +static inline bool should_mlock_folio(struct folio *folio,
> + struct vm_area_struct *vma)
> +{
> + if (vma->vm_flags & VM_LOCKED)
> + return (!folio_test_large(folio) ||
> + folio_within_vma(folio, vma));
> +
> + /*
> + * For unlock, allow munlock large folio which is partially
> + * mapped to VMA. As it's possible that large folio is
> + * mlocked and VMA is split later.
> + *
> + * During memory pressure, such kind of large folio can
> + * be split. And the pages are not in VM_LOCKed VMA
> + * can be reclaimed.
> + */
> +
> + return true;
Looks good, or just
should_mlock_folio() // or whatever name you see fit, can_mlock_folio()?
{
return !(vma->vm_flags & VM_LOCKED) || folio_within_vma();
}
> +}
> +
> +static inline unsigned int get_folio_mlock_step(struct folio *folio,
> + pte_t pte, unsigned long addr, unsigned long end)
> +{
> + unsigned int nr;
> +
> + nr = folio_pfn(folio) + folio_nr_pages(folio) - pte_pfn(pte);
> + return min_t(unsigned int, nr, (end - addr) >> PAGE_SHIFT);
> +}
> +
> +void mlock_folio_range(struct folio *folio, struct vm_area_struct *vma,
> + pte_t *pte, unsigned long addr, unsigned int nr)
> +{
> + struct folio *cow_folio;
> + unsigned int step = 1;
> +
> + mlock_folio(folio);
> + if (nr == 1)
> + return;
> +
> + for (; nr > 0; pte += step, addr += (step << PAGE_SHIFT), nr -= step) {
> + pte_t ptent;
> +
> + step = 1;
> + ptent = ptep_get(pte);
> +
> + if (!pte_present(ptent))
> + continue;
> +
> + cow_folio = vm_normal_folio(vma, addr, ptent);
> + if (!cow_folio || cow_folio == folio) {
> + continue;
> + }
> +
> + mlock_folio(cow_folio);
> + step = get_folio_mlock_step(folio, ptent,
> + addr, addr + (nr << PAGE_SHIFT));
> + }
> +}
> +
> +void munlock_folio_range(struct folio *folio, struct vm_area_struct *vma,
> + pte_t *pte, unsigned long addr, unsigned int nr)
> +{
> + struct folio *cow_folio;
> + unsigned int step = 1;
> +
> + munlock_folio(folio);
> + if (nr == 1)
> + return;
> +
> + for (; nr > 0; pte += step, addr += (step << PAGE_SHIFT), nr -= step) {
> + pte_t ptent;
> +
> + step = 1;
> + ptent = ptep_get(pte);
> +
> + if (!pte_present(ptent))
> + continue;
> +
> + cow_folio = vm_normal_folio(vma, addr, ptent);
> + if (!cow_folio || cow_folio == folio) {
> + continue;
> + }
> +
> + munlock_folio(cow_folio);
> + step = get_folio_mlock_step(folio, ptent,
> + addr, addr + (nr << PAGE_SHIFT));
> + }
> +}
I'll finish the above later.
> static int mlock_pte_range(pmd_t *pmd, unsigned long addr,
> unsigned long end, struct mm_walk *walk)
>
> @@ -314,6 +403,7 @@ static int mlock_pte_range(pmd_t *pmd, unsigned long addr,
> pte_t *start_pte, *pte;
> pte_t ptent;
> struct folio *folio;
> + unsigned int step = 1;
>
> ptl = pmd_trans_huge_lock(pmd, vma);
> if (ptl) {
> @@ -329,24 +419,28 @@ static int mlock_pte_range(pmd_t *pmd, unsigned long addr,
> goto out;
> }
>
> - start_pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> + pte = start_pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> if (!start_pte) {
> walk->action = ACTION_AGAIN;
> return 0;
> }
> - for (pte = start_pte; addr != end; pte++, addr += PAGE_SIZE) {
> +
> + for (; addr != end; pte += step, addr += (step << PAGE_SHIFT)) {
> + step = 1;
> ptent = ptep_get(pte);
> if (!pte_present(ptent))
> continue;
> folio = vm_normal_folio(vma, addr, ptent);
> if (!folio || folio_is_zone_device(folio))
> continue;
> - if (folio_test_large(folio))
> + if (!should_mlock_folio(folio, vma))
> continue;
> +
> + step = get_folio_mlock_step(folio, ptent, addr, end);
> if (vma->vm_flags & VM_LOCKED)
> - mlock_folio(folio);
> + mlock_folio_range(folio, vma, pte, addr, step);
> else
> - munlock_folio(folio);
> + munlock_folio_range(folio, vma, pte, addr, step);
> }
> pte_unmap(start_pte);
> out:
Looks good.
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