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Message-ID: <CAOUHufZQ0EpyRZ_jAMxs8uNSQOz6uAkzVjvvgD+4wBvmgHJoCA@mail.gmail.com>
Date: Wed, 12 Jul 2023 00:23:23 -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 2/3] mm: handle large folio when large folio in
VM_LOCKED VMA range
On Wed, Jul 12, 2023 at 12:02 AM Yin Fengwei <fengwei.yin@...el.com> wrote:
>
> If large folio is in the range of VM_LOCKED VMA, it should be
> mlocked to avoid being picked by page reclaim. Which may split
> the large folio and then mlock each pages again.
>
> Mlock this kind of large folio to prevent them being picked by
> page reclaim.
>
> For the large folio which cross the boundary of VM_LOCKED VMA,
> we'd better not to mlock it. So if the system is under memory
> pressure, this kind of large folio will be split and the pages
> ouf of VM_LOCKED VMA can be reclaimed.
>
> Signed-off-by: Yin Fengwei <fengwei.yin@...el.com>
> ---
> mm/internal.h | 11 ++++++++---
> mm/rmap.c | 34 +++++++++++++++++++++++++++-------
> 2 files changed, 35 insertions(+), 10 deletions(-)
>
> diff --git a/mm/internal.h b/mm/internal.h
> index c7dd15d8de3ef..776141de2797a 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -643,7 +643,8 @@ static inline void mlock_vma_folio(struct folio *folio,
> * still be set while VM_SPECIAL bits are added: so ignore it then.
> */
> if (unlikely((vma->vm_flags & (VM_LOCKED|VM_SPECIAL)) == VM_LOCKED) &&
> - (compound || !folio_test_large(folio)))
> + (compound || !folio_test_large(folio) ||
> + folio_in_range(folio, vma, vma->vm_start, vma->vm_end)))
> mlock_folio(folio);
> }
This can be simplified:
1. remove the compound parameter
2. make the if
if (unlikely((vma->vm_flags & (VM_LOCKED|VM_SPECIAL)) == VM_LOCKED) &&
folio_within_vma())
mlock_folio(folio);
> @@ -651,8 +652,12 @@ void munlock_folio(struct folio *folio);
> static inline void munlock_vma_folio(struct folio *folio,
> struct vm_area_struct *vma, bool compound)
Remove the compound parameter here too.
> {
> - if (unlikely(vma->vm_flags & VM_LOCKED) &&
> - (compound || !folio_test_large(folio)))
> + /*
> + * To handle the case that a mlocked large folio is unmapped from VMA
> + * piece by piece, allow munlock the large folio which is partially
> + * mapped to VMA.
> + */
> + if (unlikely(vma->vm_flags & VM_LOCKED))
> munlock_folio(folio);
> }
>
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 2668f5ea35342..455f415d8d9ca 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -803,6 +803,14 @@ struct folio_referenced_arg {
> unsigned long vm_flags;
> struct mem_cgroup *memcg;
> };
> +
> +static inline bool should_restore_mlock(struct folio *folio,
> + struct vm_area_struct *vma, bool pmd_mapped)
> +{
> + return !folio_test_large(folio) ||
> + pmd_mapped || folio_within_vma(folio, vma);
> +}
This is just folio_within_vma() :)
> /*
> * arg: folio_referenced_arg will be passed
> */
> @@ -816,13 +824,25 @@ static bool folio_referenced_one(struct folio *folio,
> while (page_vma_mapped_walk(&pvmw)) {
> address = pvmw.address;
>
> - if ((vma->vm_flags & VM_LOCKED) &&
> - (!folio_test_large(folio) || !pvmw.pte)) {
> - /* Restore the mlock which got missed */
> - mlock_vma_folio(folio, vma, !pvmw.pte);
> - page_vma_mapped_walk_done(&pvmw);
> - pra->vm_flags |= VM_LOCKED;
> - return false; /* To break the loop */
> + if (vma->vm_flags & VM_LOCKED) {
> + if (should_restore_mlock(folio, vma, !pvmw.pte)) {
> + /* Restore the mlock which got missed */
> + mlock_vma_folio(folio, vma, !pvmw.pte);
> + page_vma_mapped_walk_done(&pvmw);
> + pra->vm_flags |= VM_LOCKED;
> + return false; /* To break the loop */
> + } else {
There is no need for "else", or just
if (!folio_within_vma())
goto dec_pra_mapcount;
> + /*
> + * For large folio cross VMA boundaries, it's
> + * expected to be picked by page reclaim. But
> + * should skip reference of pages which are in
> + * the range of VM_LOCKED vma. As page reclaim
> + * should just count the reference of pages out
> + * the range of VM_LOCKED vma.
> + */
> + pra->mapcount--;
> + continue;
> + }
> }
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