Re: [RFC][PATCH] vmscan: report vm_flags in page_referenced()

[Minchan Kim]

On Fri, May 8, 2009 at 1:17 PM, Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote:
> On Thu, May 07, 2009 at 11:17:46PM +0800, Peter Zijlstra wrote:
>> On Thu, 2009-05-07 at 17:10 +0200, Johannes Weiner wrote:
>>
>> > > @@ -1269,8 +1270,15 @@ static void shrink_active_list(unsigned
>> > >
>> > > Â Â Â Â Â /* page_referenced clears PageReferenced */
>> > > Â Â Â Â Â if (page_mapping_inuse(page) &&
>> > > - Â Â Â Â Â Â page_referenced(page, 0, sc->mem_cgroup))
>> > > + Â Â Â Â Â Â page_referenced(page, 0, sc->mem_cgroup)) {
>> > > + Â Â Â Â Â Â Â Â struct address_space *mapping = page_mapping(page);
>> > > +
>> > > Â Â Â Â Â Â Â Â Â pgmoved++;
>> > > + Â Â Â Â Â Â Â Â if (mapping && test_bit(AS_EXEC, &mapping->flags)) {
>> > > + Â Â Â Â Â Â Â Â Â Â Â Â list_add(&page->lru, &l_active);
>> > > + Â Â Â Â Â Â Â Â Â Â Â Â continue;
>> > > + Â Â Â Â Â Â Â Â }
>> > > + Â Â Â Â }
>> >
>> > Since we walk the VMAs in page_referenced anyway, wouldn't it be
>> > better to check if one of them is executable? ÂThis would even work
>> > for executable anon pages. ÂAfter all, there are applications that cow
>> > executable mappings (sbcl and other language environments that use an
>> > executable, run-time modified core image come to mind).
>>
>> Hmm, like provide a vm_flags mask along to page_referenced() to only
>> account matching vmas... seems like a sensible idea.
>
> Here is a quick patch for your opinions. Compile tested.
>
> With the added vm_flags reporting, the mlock=>unevictable logic can
> possibly be made more straightforward.
>
> Thanks,
> Fengguang
> ---
> vmscan: report vm_flags in page_referenced()
>
> This enables more informed reclaim heuristics, eg. to protect executable
> file pages more aggressively.
>
> Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
> ---
> Âinclude/linux/rmap.h | Â Â5 +++--
> Âmm/rmap.c      Â|  30 +++++++++++++++++++++---------
> Âmm/vmscan.c     Â|  Â7 +++++--
> Â3 files changed, 29 insertions(+), 13 deletions(-)
>
> --- linux.orig/include/linux/rmap.h
> +++ linux/include/linux/rmap.h
> @@ -83,7 +83,8 @@ static inline void page_dup_rmap(struct
> Â/*
> Â* Called from mm/vmscan.c to handle paging out
> Â*/
> -int page_referenced(struct page *, int is_locked, struct mem_cgroup *cnt);
> +int page_referenced(struct page *, int is_locked,
> + Â Â Â Â Â Â Â Â Â Â Â struct mem_cgroup *cnt, unsigned long *vm_flags);
> Âint try_to_unmap(struct page *, int ignore_refs);
>
> Â/*
> @@ -128,7 +129,7 @@ int page_wrprotect(struct page *page, in
> Â#define anon_vma_prepare(vma) Â(0)
> Â#define anon_vma_link(vma) Â Â do {} while (0)
>
> -#define page_referenced(page,l,cnt) TestClearPageReferenced(page)
> +#define page_referenced(page, locked, cnt, flags) TestClearPageReferenced(page)
> Â#define try_to_unmap(page, refs) SWAP_FAIL
>
> Âstatic inline int page_mkclean(struct page *page)
> --- linux.orig/mm/rmap.c
> +++ linux/mm/rmap.c
> @@ -333,7 +333,8 @@ static int page_mapped_in_vma(struct pag
> Â* repeatedly from either page_referenced_anon or page_referenced_file.
> Â*/
> Âstatic int page_referenced_one(struct page *page,
> - Â Â Â struct vm_area_struct *vma, unsigned int *mapcount)
> + Â Â Â Â Â Â Â Â Â Â Â Â Â Â Âstruct vm_area_struct *vma,
> + Â Â Â Â Â Â Â Â Â Â Â Â Â Â Âunsigned int *mapcount)
> Â{
> Â Â Â Âstruct mm_struct *mm = vma->vm_mm;
> Â Â Â Âunsigned long address;
> @@ -385,7 +386,8 @@ out:
> Â}
>
> Âstatic int page_referenced_anon(struct page *page,
> - Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â struct mem_cgroup *mem_cont)
> + Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â struct mem_cgroup *mem_cont,
> + Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â unsigned long *vm_flags)
> Â{
> Â Â Â Âunsigned int mapcount;
> Â Â Â Âstruct anon_vma *anon_vma;
> @@ -406,6 +408,7 @@ static int page_referenced_anon(struct p
> Â Â Â Â Â Â Â Âif (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont))
> Â Â Â Â Â Â Â Â Â Â Â Âcontinue;
> Â Â Â Â Â Â Â Âreferenced += page_referenced_one(page, vma, &mapcount);
> + Â Â Â Â Â Â Â *vm_flags |= vma->vm_flags;

Sometime this vma don't contain the anon page.
That's why we need page_check_address.
For such a case, wrong *vm_flag cause be harmful to reclaim.
It can be happen in your first class citizen patch, I think.



-- 
Kinds regards,
Minchan Kim
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