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Date:   Mon, 13 Jan 2020 10:11:18 -0800
From:   Minchan Kim <minchan@kernel.org>
To:     SeongJae Park <sj38.park@gmail.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>, linux-api@vger.kernel.org,
        oleksandr@redhat.com, Suren Baghdasaryan <surenb@google.com>,
        Tim Murray <timmurray@google.com>,
        Daniel Colascione <dancol@google.com>,
        Sandeep Patil <sspatil@google.com>,
        Sonny Rao <sonnyrao@google.com>,
        Brian Geffon <bgeffon@google.com>,
        Michal Hocko <mhocko@suse.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Shakeel Butt <shakeelb@google.com>,
        John Dias <joaodias@google.com>
Subject: Re: [PATCH 1/4] mm: factor out madvise's core functionality
Message-ID: <20200113181118.GB110363@google.com>
References: <20200110213433.94739-2-minchan@kernel.org>
 <20200111073737.25321-1-sj38.park@gmail.com>
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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@kernel.org> 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@kernel.org>
> > ---
> >  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.