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SubjectRe: [PATCH 1/2] mm: use add_page_to_lru_list()/page_lru()/page_off_lru()
On Sun, Aug 30, 2020 at 04:31:38PM +0800, Alex Shi wrote:
>
>
> 在 2020/8/30 上午2:12, Yu Zhao 写道:
> > On Thu, Aug 27, 2020 at 05:42:01PM -0600, Yu Zhao wrote:
> >> This is a trivial but worth having clean-up patch. There should be
> >> no side effects except page->lru is temporarily poisoned after it's
> >> deleted but before it's added to the new list in move_pages_to_lru()
> >> (which is not a problem).
> >>
> >> Signed-off-by: Yu Zhao <yuzhao@google.com>
> >
> > Hi Alex, I just realized your
> > [v18,08/32] mm/vmscan: remove unnecessary lruvec adding
> > at
> > https://patchwork.kernel.org/patch/11733123/
> > also touches move_pages_to_lru(). I agree it's better not to add
> > a page we are going to free to the list in the first place. The
> > rest in this patch would be too trivial to be a separate one (on
> > top of yours).
> >
> > So would you mind taking of the clean-up too in your series? I'll
> > drop this one then. Thanks.

Ok, maybe I wasn't clear before. Please see what exactly I'm asking
you to consider below.

> >> diff --git a/mm/swap.c b/mm/swap.c
> >> index 40bf20a75278..2735ecf0f566 100644
> >> --- a/mm/swap.c
> >> +++ b/mm/swap.c
> >> @@ -597,11 +597,9 @@ static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec,
> >> {
> >> if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) &&
> >> !PageSwapCache(page) && !PageUnevictable(page)) {
> >> - bool active = PageActive(page);
> >> int nr_pages = thp_nr_pages(page);
> >>
> >> - del_page_from_lru_list(page, lruvec,
> >> - LRU_INACTIVE_ANON + active);
> >> + del_page_from_lru_list(page, lruvec, page_lru(page));
> >> ClearPageActive(page);
> >> ClearPageReferenced(page);
> >> /*

1) The above has no conflict with your series and therefore can go
separately. Feel free to include it.

> >> diff --git a/mm/vmscan.c b/mm/vmscan.c
> >> index 99e1796eb833..b479ced26cd3 100644
> >> --- a/mm/vmscan.c
> >> +++ b/mm/vmscan.c
> >> @@ -1845,13 +1845,12 @@ static unsigned noinline_for_stack move_pages_to_lru(struct lruvec *lruvec,
> >> int nr_pages, nr_moved = 0;
> >> LIST_HEAD(pages_to_free);
> >> struct page *page;
> >> - enum lru_list lru;
> >>
> >> while (!list_empty(list)) {
> >> page = lru_to_page(list);
> >> VM_BUG_ON_PAGE(PageLRU(page), page);
> >> + list_del(&page->lru);
> >> if (unlikely(!page_evictable(page))) {
> >> - list_del(&page->lru);
> >> spin_unlock_irq(&pgdat->lru_lock);
> >> putback_lru_page(page);
> >> spin_lock_irq(&pgdat->lru_lock);

2) The above is the same change you've made.

> >> @@ -1860,16 +1859,10 @@ static unsigned noinline_for_stack move_pages_to_lru(struct lruvec *lruvec,
> >> lruvec = mem_cgroup_page_lruvec(page, pgdat);
> >>
> >> SetPageLRU(page);
> >> - lru = page_lru(page);
> >> -
> >> - nr_pages = thp_nr_pages(page);
> >> - update_lru_size(lruvec, lru, page_zonenum(page), nr_pages);
> >> - list_move(&page->lru, &lruvec->lists[lru]);
> >> + add_page_to_lru_list(page, lruvec, page_lru(page));
> >>
> >> if (put_page_testzero(page)) {
> >> - __ClearPageLRU(page);
>
> it's interesting to know the PageLRU left has no bad impact in real life.
> it justs seems a path confliction with my that patch.

(No, we can't leave PG_lru uncleared. It's done by the page_off_lru()
right below).

> >> - __ClearPageActive(page);
> >> - del_page_from_lru_list(page, lruvec, lru);
> >> + del_page_from_lru_list(page, lruvec, page_off_lru(page));
> >>
> >> if (unlikely(PageCompound(page))) {
> >> spin_unlock_irq(&pgdat->lru_lock);
> >> @@ -1878,6 +1871,7 @@ static unsigned noinline_for_stack move_pages_to_lru(struct lruvec *lruvec,
> >> } else
> >> list_add(&page->lru, &pages_to_free);
> >> } else {
> >> + nr_pages = thp_nr_pages(page);
> >> nr_moved += nr_pages;
> >> if (PageActive(page))
> >> workingset_age_nonresident(lruvec, nr_pages);

3) The above is the conflict. Since we won't add and then delete a
page after your patch, we won't need it. But I do want this (you've
snipped from your reply, so I take that you already figured it out):

- lru = page_lru(page);
-
- nr_pages = thp_nr_pages(page);
- update_lru_size(lruvec, lru, page_zonenum(page), nr_pages);
- list_move(&page->lru, &lruvec->lists[lru]);
+ add_page_to_lru_list(page, lruvec, page_lru(page));

No worries if you prefer this to go separately too.

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