Hi, Zach,
On Tue, Apr 26, 2022 at 07:44:01AM -0700, Zach O'Keefe wrote:
> When scanning an anon pmd to see if it's eligible for collapse, return
> SCAN_PMD_MAPPED if the pmd already maps a THP. Note that
> SCAN_PMD_MAPPED is different from SCAN_PAGE_COMPOUND used in the
> file-collapse path, since the latter might identify pte-mapped compound
> pages. This is required by MADV_COLLAPSE which necessarily needs to
> know what hugepage-aligned/sized regions are already pmd-mapped.
>
> Signed-off-by: Zach O'Keefe <zokeefe@xxxxxxxxxx>
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
IIUC we don't need to attach this reported-by if this is not a bugfix. I
think you can simply fix all issues reported by the test bot and only
attach the line if the patch is fixing the problem that the bot was
reporting explicitly.
> ---
> include/trace/events/huge_memory.h | 3 ++-
> mm/internal.h | 1 +
> mm/khugepaged.c | 30 ++++++++++++++++++++++++++----
> mm/rmap.c | 15 +++++++++++++--
> 4 files changed, 42 insertions(+), 7 deletions(-)
>
> diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h
> index d651f3437367..9faa678e0a5b 100644
> --- a/include/trace/events/huge_memory.h
> +++ b/include/trace/events/huge_memory.h
> @@ -33,7 +33,8 @@
> EM( SCAN_ALLOC_HUGE_PAGE_FAIL, "alloc_huge_page_failed") \
> EM( SCAN_CGROUP_CHARGE_FAIL, "ccgroup_charge_failed") \
> EM( SCAN_TRUNCATED, "truncated") \
> - EMe(SCAN_PAGE_HAS_PRIVATE, "page_has_private") \
> + EM( SCAN_PAGE_HAS_PRIVATE, "page_has_private") \
> + EMe(SCAN_PMD_MAPPED, "page_pmd_mapped") \
Nit: IMHO it can be put even in the middle so we don't need to touch the
EMe() every time. :)
Apart from that, it does sound proper to me to put SCAN_PMD_MAPPED to be
right after SCAN_PMD_NULL anyway.
>
> #undef EM
> #undef EMe
> diff --git a/mm/internal.h b/mm/internal.h
> index 0667abd57634..51ae9f71a2a3 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -172,6 +172,7 @@ extern void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason
> /*
> * in mm/rmap.c:
> */
> +pmd_t *mm_find_pmd_raw(struct mm_struct *mm, unsigned long address);
> extern pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address);
>
> /*
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index ba8dbd1825da..2933b13fc975 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -51,6 +51,7 @@ enum scan_result {
> SCAN_CGROUP_CHARGE_FAIL,
> SCAN_TRUNCATED,
> SCAN_PAGE_HAS_PRIVATE,
> + SCAN_PMD_MAPPED,
> };
>
> #define CREATE_TRACE_POINTS
> @@ -987,6 +988,29 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
> return 0;
> }
>
> +static int find_pmd_or_thp_or_none(struct mm_struct *mm,
> + unsigned long address,
> + pmd_t **pmd)
> +{
> + pmd_t pmde;
> +
> + *pmd = mm_find_pmd_raw(mm, address);
> + if (!*pmd)
> + return SCAN_PMD_NULL;
> +
> + pmde = pmd_read_atomic(*pmd);
> +
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> + /* See comments in pmd_none_or_trans_huge_or_clear_bad() */
> + barrier();
> +#endif
> + if (!pmd_present(pmde) || pmd_none(pmde))
Could we drop the pmd_none() check? I assume !pmd_present() should have
covered that case already?
> + return SCAN_PMD_NULL;
> + if (pmd_trans_huge(pmde))
> + return SCAN_PMD_MAPPED;
> + return SCAN_SUCCEED;
> +}
> +
> /*
> * Bring missing pages in from swap, to complete THP collapse.
> * Only done if khugepaged_scan_pmd believes it is worthwhile.
> @@ -1238,11 +1262,9 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
>
> VM_BUG_ON(address & ~HPAGE_PMD_MASK);
>
> - pmd = mm_find_pmd(mm, address);
> - if (!pmd) {
> - result = SCAN_PMD_NULL;
> + result = find_pmd_or_thp_or_none(mm, address, &pmd);
> + if (result != SCAN_SUCCEED)
> goto out;
> - }
>
> memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
> pte = pte_offset_map_lock(mm, pmd, address, &ptl);
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 61e63db5dc6f..49817f35e65c 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -759,13 +759,12 @@ unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
> return vma_address(page, vma);
> }
>
> -pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address)
> +pmd_t *mm_find_pmd_raw(struct mm_struct *mm, unsigned long address)
> {
> pgd_t *pgd;
> p4d_t *p4d;
> pud_t *pud;
> pmd_t *pmd = NULL;
> - pmd_t pmde;
>
> pgd = pgd_offset(mm, address);
> if (!pgd_present(*pgd))
> @@ -780,6 +779,18 @@ pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address)
> goto out;
>
> pmd = pmd_offset(pud, address);
> +out:
> + return pmd;
> +}
> +
> +pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address)
> +{
> + pmd_t pmde;
> + pmd_t *pmd;
> +
> + pmd = mm_find_pmd_raw(mm, address);
> + if (!pmd)
> + goto out;
> /*
> * Some THP functions use the sequence pmdp_huge_clear_flush(), set_pmd_at()
> * without holding anon_vma lock for write. So when looking for a
> --
> 2.36.0.rc2.479.g8af0fa9b8e-goog
>
--
Peter Xu
