On Mon, 24 Aug 2020, Alex Shi wrote: > Hugh Dickins' found a memcg change bug on original version: > If we want to change the pgdat->lru_lock to memcg's lruvec lock, we have > to serialize mem_cgroup_move_account during pagevec_lru_move_fn. The > possible bad scenario would like: > > cpu 0 cpu 1 > lruvec = mem_cgroup_page_lruvec() > if (!isolate_lru_page()) > mem_cgroup_move_account > > spin_lock_irqsave(&lruvec->lru_lock <== wrong lock. > > So we need the ClearPageLRU to block isolate_lru_page(), that serializes
s/the ClearPageLRU/TestClearPageLRU/ > the memcg change. and then removing the PageLRU check in move_fn callee > as the consequence. Deserves another paragraph about __pagevec_lru_add(): "__pagevec_lru_add_fn() is different from the others, because the pages it deals with are, by definition, not yet on the lru. TestClearPageLRU is not needed and would not work, so __pagevec_lru_add() goes its own way." > > Reported-by: Hugh Dickins <[email protected]> True. > Signed-off-by: Hugh Dickins <[email protected]> I did provide some lines, but I think it's just Acked-by: Hugh Dickins <[email protected]> to go below your Signed-off-by. > Signed-off-by: Alex Shi <[email protected]> > Cc: Andrew Morton <[email protected]> > Cc: [email protected] > Cc: [email protected] > --- > mm/swap.c | 44 +++++++++++++++++++++++++++++++++++--------- > 1 file changed, 35 insertions(+), 9 deletions(-) In your lruv19 branch, this patch got renamed (s/moveing/moving/): but I think it's better with the old name used here in v18, and without those mm/vmscan.c mods to check_move_unevictable_pages() tacked on: please move those back to 16/32, which already makes changes to vmscan.c. > > diff --git a/mm/swap.c b/mm/swap.c > index 446ffe280809..2d9a86bf93a4 100644 > --- a/mm/swap.c > +++ b/mm/swap.c > @@ -221,8 +221,14 @@ static void pagevec_lru_move_fn(struct pagevec *pvec, > spin_lock_irqsave(&pgdat->lru_lock, flags); > } > > + /* block memcg migration during page moving between lru */ > + if (!TestClearPageLRU(page)) > + continue; > + > lruvec = mem_cgroup_page_lruvec(page, pgdat); > (*move_fn)(page, lruvec); > + > + SetPageLRU(page); > } > if (pgdat) > spin_unlock_irqrestore(&pgdat->lru_lock, flags); > @@ -232,7 +238,7 @@ static void pagevec_lru_move_fn(struct pagevec *pvec, > > static void pagevec_move_tail_fn(struct page *page, struct lruvec *lruvec) > { > - if (PageLRU(page) && !PageUnevictable(page)) { > + if (!PageUnevictable(page)) { > del_page_from_lru_list(page, lruvec, page_lru(page)); > ClearPageActive(page); > add_page_to_lru_list_tail(page, lruvec, page_lru(page)); > @@ -306,7 +312,7 @@ void lru_note_cost_page(struct page *page) > > static void __activate_page(struct page *page, struct lruvec *lruvec) > { > - if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) { > + if (!PageActive(page) && !PageUnevictable(page)) { > int lru = page_lru_base_type(page); > int nr_pages = thp_nr_pages(page); > > @@ -362,7 +368,8 @@ void activate_page(struct page *page) > > page = compound_head(page); > spin_lock_irq(&pgdat->lru_lock); > - __activate_page(page, mem_cgroup_page_lruvec(page, pgdat)); > + if (PageLRU(page)) > + __activate_page(page, mem_cgroup_page_lruvec(page, pgdat)); > spin_unlock_irq(&pgdat->lru_lock); > } > #endif Every time I look at this, I wonder if that's right, or an unnecessary optimization strayed in, or whatever. For the benefit of others looking at this patch, yes it is right: this is the !CONFIG_SMP alternative version of activate_page(), and needs that PageLRU check to compensate for the check that has now been removed from __activate_page() itself. > @@ -521,9 +528,6 @@ static void lru_deactivate_file_fn(struct page *page, > struct lruvec *lruvec) > bool active; > int nr_pages = thp_nr_pages(page); > > - if (!PageLRU(page)) > - return; > - > if (PageUnevictable(page)) > return; > > @@ -564,7 +568,7 @@ static void lru_deactivate_file_fn(struct page *page, > struct lruvec *lruvec) > > static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec) > { > - if (PageLRU(page) && PageActive(page) && !PageUnevictable(page)) { > + if (PageActive(page) && !PageUnevictable(page)) { > int lru = page_lru_base_type(page); > int nr_pages = thp_nr_pages(page); > > @@ -581,7 +585,7 @@ static void lru_deactivate_fn(struct page *page, struct > lruvec *lruvec) > > static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec) > { > - if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) && > + if (PageAnon(page) && PageSwapBacked(page) && > !PageSwapCache(page) && !PageUnevictable(page)) { > bool active = PageActive(page); > int nr_pages = thp_nr_pages(page); > @@ -979,7 +983,29 @@ static void __pagevec_lru_add_fn(struct page *page, > struct lruvec *lruvec) > */ > void __pagevec_lru_add(struct pagevec *pvec) > { > - pagevec_lru_move_fn(pvec, __pagevec_lru_add_fn); > + int i; > + struct pglist_data *pgdat = NULL; > + struct lruvec *lruvec; > + unsigned long flags = 0; > + > + for (i = 0; i < pagevec_count(pvec); i++) { > + struct page *page = pvec->pages[i]; > + struct pglist_data *pagepgdat = page_pgdat(page); > + > + if (pagepgdat != pgdat) { > + if (pgdat) > + spin_unlock_irqrestore(&pgdat->lru_lock, flags); > + pgdat = pagepgdat; > + spin_lock_irqsave(&pgdat->lru_lock, flags); > + } > + > + lruvec = mem_cgroup_page_lruvec(page, pgdat); > + __pagevec_lru_add_fn(page, lruvec); > + } > + if (pgdat) > + spin_unlock_irqrestore(&pgdat->lru_lock, flags); > + release_pages(pvec->pages, pvec->nr); > + pagevec_reinit(pvec); > } > > /** > -- > 1.8.3.1
