Re: [RFCv2 4/6] mm: factor out madvise's core functionality

From: Oleksandr Natalenko
Date: Fri May 31 2019 - 03:08:05 EST

On Fri, May 31, 2019 at 03:43:11PM +0900, Minchan Kim wrote:
> This patch factor out madvise's core functionality so that upcoming
> patch can reuse it without duplication. It shouldn't change any behavior.
>
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
> ---
> mm/madvise.c | 188 +++++++++++++++++++++++++++------------------------
> 1 file changed, 101 insertions(+), 87 deletions(-)
>
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 9d749a1420b4..466623ea8c36 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -425,9 +425,10 @@ static int madvise_pageout_pte_range(pmd_t *pmd, unsigned long addr,
> struct page *page;
> int isolated = 0;
> struct vm_area_struct *vma = walk->vma;
> + struct task_struct *task = walk->private;
> unsigned long next;
>
> - if (fatal_signal_pending(current))
> + if (fatal_signal_pending(task))
> return -EINTR;
>
> next = pmd_addr_end(addr, end);
> @@ -505,12 +506,14 @@ static int madvise_pageout_pte_range(pmd_t *pmd, unsigned long addr,
> }
>
> static void madvise_pageout_page_range(struct mmu_gather *tlb,
> - struct vm_area_struct *vma,
> - unsigned long addr, unsigned long end)
> + struct task_struct *task,
> + struct vm_area_struct *vma,
> + unsigned long addr, unsigned long end)
> {
> struct mm_walk warm_walk = {
> .pmd_entry = madvise_pageout_pte_range,
> .mm = vma->vm_mm,
> + .private = task,
> };
>
> tlb_start_vma(tlb, vma);
> @@ -519,9 +522,9 @@ static void madvise_pageout_page_range(struct mmu_gather *tlb,
> }
>
>
> -static long madvise_pageout(struct vm_area_struct *vma,
> - struct vm_area_struct **prev,
> - unsigned long start_addr, unsigned long end_addr)
> +static long madvise_pageout(struct task_struct *task,
> + struct vm_area_struct *vma, struct vm_area_struct **prev,
> + unsigned long start_addr, unsigned long end_addr)
> {
> struct mm_struct *mm = vma->vm_mm;
> struct mmu_gather tlb;
> @@ -532,7 +535,7 @@ static long madvise_pageout(struct vm_area_struct *vma,
>
> lru_add_drain();
> tlb_gather_mmu(&tlb, mm, start_addr, end_addr);
> - madvise_pageout_page_range(&tlb, vma, start_addr, end_addr);
> + madvise_pageout_page_range(&tlb, task, vma, start_addr, end_addr);
> tlb_finish_mmu(&tlb, start_addr, end_addr);
>
> return 0;
> @@ -744,7 +747,8 @@ static long madvise_dontneed_single_vma(struct vm_area_struct *vma,
> return 0;
> }
>
> -static long madvise_dontneed_free(struct vm_area_struct *vma,
> +static long madvise_dontneed_free(struct mm_struct *mm,
> + struct vm_area_struct *vma,
> struct vm_area_struct **prev,
> unsigned long start, unsigned long end,
> int behavior)
> @@ -756,8 +760,8 @@ static long madvise_dontneed_free(struct vm_area_struct *vma,
> if (!userfaultfd_remove(vma, start, end)) {
> *prev = NULL; /* mmap_sem has been dropped, prev is stale */
>
> - down_read(&current->mm->mmap_sem);
> - vma = find_vma(current->mm, start);
> + down_read(&mm->mmap_sem);
> + vma = find_vma(mm, start);
> if (!vma)
> return -ENOMEM;
> if (start < vma->vm_start) {
> @@ -804,7 +808,8 @@ static long madvise_dontneed_free(struct vm_area_struct *vma,
> * Application wants to free up the pages and associated backing store.
> * This is effectively punching a hole into the middle of a file.
> */
> -static long madvise_remove(struct vm_area_struct *vma,
> +static long madvise_remove(struct mm_struct *mm,
> + struct vm_area_struct *vma,
> struct vm_area_struct **prev,
> unsigned long start, unsigned long end)
> {
> @@ -838,13 +843,13 @@ static long madvise_remove(struct vm_area_struct *vma,
> get_file(f);
> if (userfaultfd_remove(vma, start, end)) {
> /* mmap_sem was not released by userfaultfd_remove() */
> - up_read(&current->mm->mmap_sem);
> + up_read(&mm->mmap_sem);
> }
> error = vfs_fallocate(f,
> FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
> offset, end - start);
> fput(f);
> - down_read(&current->mm->mmap_sem);
> + down_read(&mm->mmap_sem);
> return error;
> }
>
> @@ -918,21 +923,23 @@ static int madvise_inject_error(int behavior,
> #endif
>
> static long
> -madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
> +madvise_vma(struct task_struct *task, struct mm_struct *mm,
> + struct vm_area_struct *vma, struct vm_area_struct **prev,
> unsigned long start, unsigned long end, int behavior)
> {
> switch (behavior) {
> case MADV_REMOVE:
> - return madvise_remove(vma, prev, start, end);
> + return madvise_remove(mm, vma, prev, start, end);
> case MADV_WILLNEED:
> return madvise_willneed(vma, prev, start, end);
> case MADV_COLD:
> return madvise_cold(vma, prev, start, end);
> case MADV_PAGEOUT:
> - return madvise_pageout(vma, prev, start, end);
> + return madvise_pageout(task, vma, prev, start, end);
> case MADV_FREE:
> case MADV_DONTNEED:
> - return madvise_dontneed_free(vma, prev, start, end, behavior);
> + return madvise_dontneed_free(mm, vma, prev, start,
> + end, behavior);
> default:
> return madvise_behavior(vma, prev, start, end, behavior);
> }
> @@ -976,68 +983,8 @@ madvise_behavior_valid(int behavior)
> }
> }
>
> -/*
> - * The madvise(2) system call.
> - *
> - * Applications can use madvise() to advise the kernel how it should
> - * handle paging I/O in this VM area. The idea is to help the kernel
> - * use appropriate read-ahead and caching techniques. The information
> - * provided is advisory only, and can be safely disregarded by the
> - * kernel without affecting the correct operation of the application.
> - *
> - * behavior values:
> - * MADV_NORMAL - the default behavior is to read clusters. This
> - * results in some read-ahead and read-behind.
> - * MADV_RANDOM - the system should read the minimum amount of data
> - * on any access, since it is unlikely that the appli-
> - * cation will need more than what it asks for.
> - * MADV_SEQUENTIAL - pages in the given range will probably be accessed
> - * once, so they can be aggressively read ahead, and
> - * can be freed soon after they are accessed.
> - * MADV_WILLNEED - the application is notifying the system to read
> - * some pages ahead.
> - * MADV_DONTNEED - the application is finished with the given range,
> - * so the kernel can free resources associated with it.
> - * MADV_FREE - the application marks pages in the given range as lazy free,
> - * where actual purges are postponed until memory pressure happens.
> - * MADV_REMOVE - the application wants to free up the given range of
> - * pages and associated backing store.
> - * MADV_DONTFORK - omit this area from child's address space when forking:
> - * typically, to avoid COWing pages pinned by get_user_pages().
> - * MADV_DOFORK - cancel MADV_DONTFORK: no longer omit this area when forking.
> - * MADV_WIPEONFORK - present the child process with zero-filled memory in this
> - * range after a fork.
> - * MADV_KEEPONFORK - undo the effect of MADV_WIPEONFORK
> - * MADV_HWPOISON - trigger memory error handler as if the given memory range
> - * were corrupted by unrecoverable hardware memory failure.
> - * MADV_SOFT_OFFLINE - try to soft-offline the given range of memory.
> - * MADV_MERGEABLE - the application recommends that KSM try to merge pages in
> - * this area with pages of identical content from other such areas.
> - * MADV_UNMERGEABLE- cancel MADV_MERGEABLE: no longer merge pages with others.
> - * MADV_HUGEPAGE - the application wants to back the given range by transparent
> - * huge pages in the future. Existing pages might be coalesced and
> - * new pages might be allocated as THP.
> - * MADV_NOHUGEPAGE - mark the given range as not worth being backed by
> - * transparent huge pages so the existing pages will not be
> - * coalesced into THP and new pages will not be allocated as THP.
> - * MADV_DONTDUMP - the application wants to prevent pages in the given range
> - * from being included in its core dump.
> - * MADV_DODUMP - cancel MADV_DONTDUMP: no longer exclude from core dump.
> - *
> - * return values:
> - * zero - success
> - * -EINVAL - start + len < 0, start is not page-aligned,
> - * "behavior" is not a valid value, or application
> - * is attempting to release locked or shared pages,
> - * or the specified address range includes file, Huge TLB,
> - * MAP_SHARED or VMPFNMAP range.
> - * -ENOMEM - addresses in the specified range are not currently
> - * mapped, or are outside the AS of the process.
> - * -EIO - an I/O error occurred while paging in data.
> - * -EBADF - map exists, but area maps something that isn't a file.
> - * -EAGAIN - a kernel resource was temporarily unavailable.
> - */
> -SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
> +static int madvise_core(struct task_struct *task, struct mm_struct *mm,
> + unsigned long start, size_t len_in, int behavior)

Just a minor nitpick, but can we please have it named madvise_common,
not madvise_core? This would follow a usual naming scheme, when some
common functionality is factored out (like, for mutexes, semaphores
etc), and within the kernel "core" usually means something completely
different.

> {
> unsigned long end, tmp;
> struct vm_area_struct *vma, *prev;
> @@ -1068,15 +1015,16 @@ SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
>
> #ifdef CONFIG_MEMORY_FAILURE
> if (behavior == MADV_HWPOISON || behavior == MADV_SOFT_OFFLINE)
> - return madvise_inject_error(behavior, start, start + len_in);
> + return madvise_inject_error(behavior,
> + start, start + len_in);

Not sure what this change is about except changing the line length.
Note, madvise_inject_error() still operates on "current" through
get_user_pages_fast() and gup_pgd_range(), but that was not changed
here. I Know you've filtered out this hint later, so technically this
is not an issue, but, maybe, this needs some attention too since we've
already spotted it?

> #endif
>
> write = madvise_need_mmap_write(behavior);
> if (write) {
> - if (down_write_killable(&current->mm->mmap_sem))
> + if (down_write_killable(&mm->mmap_sem))
> return -EINTR;

Do you still need that trick with mmget_still_valid() here?
Something like:

if (current->mm != mm && !mmget_still_valid(mm))
goto skip_mm;

and that skip_mm label would be before

if (write)
up_write(&mm->mmap_sem);

below.

(see 04f5866e41fb70690e28397487d8bd8eea7d712a for details on this)

> } else {
> - down_read(&current->mm->mmap_sem);
> + down_read(&mm->mmap_sem);
> }
>
> /*
> @@ -1084,7 +1032,7 @@ SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
> * ranges, just ignore them, but return -ENOMEM at the end.
> * - different from the way of handling in mlock etc.
> */
> - vma = find_vma_prev(current->mm, start, &prev);
> + vma = find_vma_prev(mm, start, &prev);
> if (vma && start > vma->vm_start)
> prev = vma;
>
> @@ -1109,7 +1057,7 @@ SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
> tmp = end;
>
> /* Here vma->vm_start <= start < tmp <= (end|vma->vm_end). */
> - error = madvise_vma(vma, &prev, start, tmp, behavior);
> + error = madvise_vma(task, mm, vma, &prev, start, tmp, behavior);
> if (error)
> goto out;
> start = tmp;
> @@ -1121,14 +1069,80 @@ SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
> if (prev)
> vma = prev->vm_next;
> else /* madvise_remove dropped mmap_sem */
> - vma = find_vma(current->mm, start);
> + vma = find_vma(mm, start);
> }
> out:
> blk_finish_plug(&plug);

skip_mm:

> if (write)
> - up_write(&current->mm->mmap_sem);
> + up_write(&mm->mmap_sem);
> else
> - up_read(&current->mm->mmap_sem);
> + up_read(&mm->mmap_sem);
>
> return error;
> }
> +
> +/*
> + * The madvise(2) system call.
> + *
> + * Applications can use madvise() to advise the kernel how it should
> + * handle paging I/O in this VM area. The idea is to help the kernel
> + * use appropriate read-ahead and caching techniques. The information
> + * provided is advisory only, and can be safely disregarded by the
> + * kernel without affecting the correct operation of the application.
> + *
> + * behavior values:
> + * MADV_NORMAL - the default behavior is to read clusters. This
> + * results in some read-ahead and read-behind.
> + * MADV_RANDOM - the system should read the minimum amount of data
> + * on any access, since it is unlikely that the appli-
> + * cation will need more than what it asks for.
> + * MADV_SEQUENTIAL - pages in the given range will probably be accessed
> + * once, so they can be aggressively read ahead, and
> + * can be freed soon after they are accessed.
> + * MADV_WILLNEED - the application is notifying the system to read
> + * some pages ahead.
> + * MADV_DONTNEED - the application is finished with the given range,
> + * so the kernel can free resources associated with it.
> + * MADV_FREE - the application marks pages in the given range as lazy free,
> + * where actual purges are postponed until memory pressure happens.
> + * MADV_REMOVE - the application wants to free up the given range of
> + * pages and associated backing store.
> + * MADV_DONTFORK - omit this area from child's address space when forking:
> + * typically, to avoid COWing pages pinned by get_user_pages().
> + * MADV_DOFORK - cancel MADV_DONTFORK: no longer omit this area when forking.
> + * MADV_WIPEONFORK - present the child process with zero-filled memory in this
> + * range after a fork.
> + * MADV_KEEPONFORK - undo the effect of MADV_WIPEONFORK
> + * MADV_HWPOISON - trigger memory error handler as if the given memory range
> + * were corrupted by unrecoverable hardware memory failure.
> + * MADV_SOFT_OFFLINE - try to soft-offline the given range of memory.
> + * MADV_MERGEABLE - the application recommends that KSM try to merge pages in
> + * this area with pages of identical content from other such areas.
> + * MADV_UNMERGEABLE- cancel MADV_MERGEABLE: no longer merge pages with others.
> + * MADV_HUGEPAGE - the application wants to back the given range by transparent
> + * huge pages in the future. Existing pages might be coalesced and
> + * new pages might be allocated as THP.
> + * MADV_NOHUGEPAGE - mark the given range as not worth being backed by
> + * transparent huge pages so the existing pages will not be
> + * coalesced into THP and new pages will not be allocated as THP.
> + * MADV_DONTDUMP - the application wants to prevent pages in the given range
> + * from being included in its core dump.
> + * MADV_DODUMP - cancel MADV_DONTDUMP: no longer exclude from core dump.
> + *
> + * return values:
> + * zero - success
> + * -EINVAL - start + len < 0, start is not page-aligned,
> + * "behavior" is not a valid value, or application
> + * is attempting to release locked or shared pages,
> + * or the specified address range includes file, Huge TLB,
> + * MAP_SHARED or VMPFNMAP range.
> + * -ENOMEM - addresses in the specified range are not currently
> + * mapped, or are outside the AS of the process.
> + * -EIO - an I/O error occurred while paging in data.
> + * -EBADF - map exists, but area maps something that isn't a file.
> + * -EAGAIN - a kernel resource was temporarily unavailable.
> + */
> +SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
> +{
> + return madvise_core(current, current->mm, start, len_in, behavior);
> +}
> --
> 2.22.0.rc1.257.g3120a18244-goog
>

--
Best regards,
Oleksandr Natalenko (post-factum)
Senior Software Maintenance Engineer