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SubjectRe: [patch 1/3] vmscan: factor out page reference checks
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Hi, Hannes. 

On Mon, 2010-02-22 at 20:49 +0100, Johannes Weiner wrote:
> Moving the big conditional into its own predicate function makes the
> code a bit easier to read and allows for better commenting on the
> checks one-by-one.
>
> This is just cleaning up, no semantics should have been changed.
>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> ---
> mm/vmscan.c | 53 ++++++++++++++++++++++++++++++++++++++++-------------
> 1 files changed, 40 insertions(+), 13 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index c26986c..c2db55b 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -579,6 +579,37 @@ redo:
> put_page(page); /* drop ref from isolate */
> }
>
> +enum page_references {
> + PAGEREF_RECLAIM,
> + PAGEREF_RECLAIM_CLEAN,
> + PAGEREF_ACTIVATE,
> +};
> +
> +static enum page_references page_check_references(struct page *page,
> + struct scan_control *sc)
> +{
> + unsigned long vm_flags;
> + int referenced;
> +
> + referenced = page_referenced(page, 1, sc->mem_cgroup, &vm_flags);
> + if (!referenced)
> + return PAGEREF_RECLAIM;
> +
> + /* Lumpy reclaim - ignore references */
> + if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
> + return PAGEREF_RECLAIM;
> +
> + /* Mlock lost isolation race - let try_to_unmap() handle it */

How doest try_to_unamp handle it?

/* Page which PG_mlocked lost isolation race - let try_to_unmap() move
the page to unevitable list */
The point is to move the page into unevictable list in case of race.
Let's write down comment more clearly.
As it was, it was clear, I think. :)

> + if (vm_flags & VM_LOCKED)
> + return PAGEREF_RECLAIM;
> +
> + if (page_mapping_inuse(page))
> + return PAGEREF_ACTIVATE;
> +
> + /* Reclaim if clean, defer dirty pages to writeback */
> + return PAGEREF_RECLAIM_CLEAN;
> +}
> +
> /*
> * shrink_page_list() returns the number of reclaimed pages
> */
> @@ -590,16 +621,15 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> struct pagevec freed_pvec;
> int pgactivate = 0;
> unsigned long nr_reclaimed = 0;
> - unsigned long vm_flags;
>
> cond_resched();
>
> pagevec_init(&freed_pvec, 1);
> while (!list_empty(page_list)) {
> + enum page_references references;
> struct address_space *mapping;
> struct page *page;
> int may_enter_fs;
> - int referenced;
>
> cond_resched();
>
> @@ -641,17 +671,14 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> goto keep_locked;
> }
>
> - referenced = page_referenced(page, 1,
> - sc->mem_cgroup, &vm_flags);
> - /*
> - * In active use or really unfreeable? Activate it.
> - * If page which have PG_mlocked lost isoltation race,
> - * try_to_unmap moves it to unevictable list
> - */
> - if (sc->order <= PAGE_ALLOC_COSTLY_ORDER &&
> - referenced && page_mapping_inuse(page)
> - && !(vm_flags & VM_LOCKED))
> + references = page_check_references(page, sc);
> + switch (references) {
> + case PAGEREF_ACTIVATE:
> goto activate_locked;
> + case PAGEREF_RECLAIM:
> + case PAGEREF_RECLAIM_CLEAN:
> + ; /* try to reclaim the page below */
> + }
>
> /*
> * Anonymous process memory has backing store?
> @@ -685,7 +712,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> }
>
> if (PageDirty(page)) {
> - if (sc->order <= PAGE_ALLOC_COSTLY_ORDER && referenced)
> + if (references == PAGEREF_RECLAIM_CLEAN)

How equal PAGEREF_RECLAIM_CLEAN and sc->order <= PAGE_ALLOC_COSTLY_ORDER
&& referenced by semantic?
Dirtyness test is already done above line by PageDirty.
So I think PAGEREF_RECLAIM_CLEAN isn't proper in there.
What's your intention I don't catch?


> goto keep_locked;
> if (!may_enter_fs)
> goto keep_locked;


--
Kind regards,
Minchan Kim




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