Re: [PATCH 1/4] mm: factor out madvise's core functionality

From: Minchan Kim
Date: Mon Jan 13 2020 - 13:11:26 EST

On Sat, Jan 11, 2020 at 08:37:37AM +0100, SeongJae Park wrote:
> On Fri, 10 Jan 2020 13:34:30 -0800 Minchan Kim <minchan@xxxxxxxxxx> 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 | 194 +++++++++++++++++++++++++++++----------------------
> > 1 file changed, 111 insertions(+), 83 deletions(-)
> >
> > diff --git a/mm/madvise.c b/mm/madvise.c
> > index bcdb6a042787..0c901de531e4 100644
> > --- a/mm/madvise.c
> > +++ b/mm/madvise.c
> > @@ -35,6 +35,7 @@
> > struct madvise_walk_private {
> > struct mmu_gather *tlb;
> > bool pageout;
> > + struct task_struct *task;
> > };
> >
> > /*
> > @@ -306,12 +307,13 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
> > bool pageout = private->pageout;
> > struct mm_struct *mm = tlb->mm;
> > struct vm_area_struct *vma = walk->vma;
> > + struct task_struct *task = private->task;
> > pte_t *orig_pte, *pte, ptent;
> > spinlock_t *ptl;
> > struct page *page = NULL;
> > LIST_HEAD(page_list);
> >
> > - if (fatal_signal_pending(current))
> > + if (fatal_signal_pending(task))
> > return -EINTR;
> >
> > #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > @@ -469,12 +471,14 @@ static const struct mm_walk_ops cold_walk_ops = {
> > };
> >
> > static void madvise_cold_page_range(struct mmu_gather *tlb,
> > + struct task_struct *task,
> > struct vm_area_struct *vma,
> > unsigned long addr, unsigned long end)
> > {
> > struct madvise_walk_private walk_private = {
> > .pageout = false,
> > .tlb = tlb,
> > + .task = task,
> > };
> >
> > tlb_start_vma(tlb, vma);
> > @@ -482,7 +486,7 @@ static void madvise_cold_page_range(struct mmu_gather *tlb,
> > tlb_end_vma(tlb, vma);
> > }
> >
> > -static long madvise_cold(struct vm_area_struct *vma,
> > +static long madvise_cold(struct task_struct *task, struct vm_area_struct *vma,
> > struct vm_area_struct **prev,
> > unsigned long start_addr, unsigned long end_addr)
> > {
> > @@ -495,19 +499,21 @@ static long madvise_cold(struct vm_area_struct *vma,
> >
> > lru_add_drain();
> > tlb_gather_mmu(&tlb, mm, start_addr, end_addr);
> > - madvise_cold_page_range(&tlb, vma, start_addr, end_addr);
> > + madvise_cold_page_range(&tlb, task, vma, start_addr, end_addr);
> > tlb_finish_mmu(&tlb, start_addr, end_addr);
> >
> > return 0;
> > }
> >
> > static void madvise_pageout_page_range(struct mmu_gather *tlb,
> > + struct task_struct *task,
> > struct vm_area_struct *vma,
> > unsigned long addr, unsigned long end)
> > {
> > struct madvise_walk_private walk_private = {
> > .pageout = true,
> > .tlb = tlb,
> > + .task = task,
> > };
> >
> > tlb_start_vma(tlb, vma);
> > @@ -531,9 +537,9 @@ static inline bool can_do_pageout(struct vm_area_struct *vma)
> > inode_permission(file_inode(vma->vm_file), MAY_WRITE) == 0;
> > }
> >
> > -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;
> > @@ -547,7 +553,7 @@ 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;
> > @@ -751,7 +757,8 @@ 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)
> > @@ -763,8 +770,8 @@ 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) {
> > @@ -811,7 +818,8 @@ 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)
> > {
> > @@ -845,13 +853,13 @@ 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;
> > }
> >
> > @@ -925,21 +933,23 @@ 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);
> > + return madvise_cold(task, 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);
> > }
> > @@ -984,67 +994,19 @@ madvise_behavior_valid(int behavior)
> > }
> >
> > /*
> > - * The madvise(2) system call.
> > + * madvise_common - request behavior hint to address range of the target process
> > *
> > - * 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.
> > + * @task: task_struct got behavior hint, not giving the hint
> > + * @mm: mm_struct got behavior hint, not giving the hint
> > + * @start: base address of the hinted range
> > + * @len_in: length of the hinted range
> > + * @behavior: requested hint
> > *
> > - * 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.
> > + * @task could be a zombie leader if it calls sys_exit so accessing mm_struct
> > + * via task->mm is prohibited. Please use @mm instead of task->mm.
> > */
> > -SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
> > +static int madvise_common(struct task_struct *task, struct mm_struct *mm,
> > + unsigned long start, size_t len_in, int behavior)
> > {
> > unsigned long end, tmp;
> > struct vm_area_struct *vma, *prev;
> > @@ -1082,10 +1044,10 @@ SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
> >
> > 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;
> > } else {
> > - down_read(&current->mm->mmap_sem);
> > + down_read(&mm->mmap_sem);
> > }
> >
> > /*
> > @@ -1093,7 +1055,7 @@ 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;
> >
> > @@ -1118,7 +1080,7 @@ 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;
> > @@ -1130,14 +1092,80 @@ 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);
> > 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.
>
> Just a trivial suggestion. How about adding brief descriptions for the
> 'MADV_COLD' and 'MADV_PAGEOUT' here, probably with another patch?

How about this?
Feel free to suggest better wording.

diff --git a/mm/madvise.c b/mm/madvise.c
index 3aa9aec6bfd9..78b3ab789486 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1169,6 +1169,10 @@ static int madvise_common(struct task_struct *task, struct mm_struct *mm,
* 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.
+ * MADV_COLD - the application uses the memory less so the kernel can deactivate
+ * the memory to evict them quickly when the memory pressure happen.
+ * MADV_PAGEOUT - the application uses the memroy very rarely so kernel can
+ * page out the memory instantly.
*
* return values:
* zero - success

Thanks.