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SubjectRe: [PATCH 3/3] mm,thp,shmem: make khugepaged obey tmpfs mount flags
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On 11/24/20 8:49 PM, Rik van Riel wrote:
> Currently if thp enabled=[madvise], mounting a tmpfs filesystem
> with huge=always and mmapping files from that tmpfs does not
> result in khugepaged collapsing those mappings, despite the
> mount flag indicating that it should.
>
> Fix that by breaking up the blocks of tests in hugepage_vma_check
> a little bit, and testing things in the correct order.
>
> Signed-off-by: Rik van Riel <riel@surriel.com>
> Fixes: c2231020ea7b ("mm: thp: register mm for khugepaged when merging vma for shmem")

Looks ok. But, it we have sysfs thp enabled=never, and shmem mount explicitly
thp enabled, then shmem mount overrides the global sysfs setting and thp's will
be allocated there, right? However, khugepaged_enabled() will be false and thus
khugepaged won't run at all? So a similar situation than what you're fixing here.

> ---
> include/linux/khugepaged.h | 2 ++
> mm/khugepaged.c | 22 ++++++++++++++++------
> 2 files changed, 18 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/khugepaged.h b/include/linux/khugepaged.h
> index c941b7377321..2fcc01891b47 100644
> --- a/include/linux/khugepaged.h
> +++ b/include/linux/khugepaged.h
> @@ -3,6 +3,7 @@
> #define _LINUX_KHUGEPAGED_H
>
> #include <linux/sched/coredump.h> /* MMF_VM_HUGEPAGE */
> +#include <linux/shmem_fs.h>
>
>
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> @@ -57,6 +58,7 @@ static inline int khugepaged_enter(struct vm_area_struct *vma,
> {
> if (!test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags))
> if ((khugepaged_always() ||
> + (shmem_file(vma->vm_file) && shmem_huge_enabled(vma)) ||
> (khugepaged_req_madv() && (vm_flags & VM_HUGEPAGE))) &&
> !(vm_flags & VM_NOHUGEPAGE) &&
> !test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 4e3dff13eb70..abab394c4206 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -440,18 +440,28 @@ static inline int khugepaged_test_exit(struct mm_struct *mm)
> static bool hugepage_vma_check(struct vm_area_struct *vma,
> unsigned long vm_flags)
> {
> - if ((!(vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
> - (vm_flags & VM_NOHUGEPAGE) ||
> + /* Explicitly disabled through madvise. */
> + if ((vm_flags & VM_NOHUGEPAGE) ||
> test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
> return false;
>
> - if (shmem_file(vma->vm_file) ||
> - (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
> - vma->vm_file &&
> - (vm_flags & VM_DENYWRITE))) {
> + /* Enabled via shmem mount options or sysfs settings. */
> + if (shmem_file(vma->vm_file) && shmem_huge_enabled(vma)) {
> return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
> HPAGE_PMD_NR);
> }
> +
> + /* THP settings require madvise. */
> + if (!(vm_flags & VM_HUGEPAGE) && !khugepaged_always())
> + return false;
> +
> + /* Read-only file mappings need to be aligned for THP to work. */
> + if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && vma->vm_file &&
> + (vm_flags & VM_DENYWRITE)) {
> + return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
> + HPAGE_PMD_NR);
> + }
> +
> if (!vma->anon_vma || vma->vm_ops)
> return false;
> if (vma_is_temporary_stack(vma))
>

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