Re: [PATCH v16 13/22] mm/lru: introduce TestClearPageLRU

[Alex Shi <alex.shi@linux.alibaba.com>]

Hi Johannes,

The patchset looks good from logical and testing part. Is there any concern
for any patches?

Thanks
Alex

在 2020/7/11 上午8:58, Alex Shi 写道:
> Combine PageLRU check and ClearPageLRU into a function by new
> introduced func TestClearPageLRU. This function will be used as page
> isolation precondition to prevent other isolations some where else.
> Then there are may non PageLRU page on lru list, need to remove BUG
> checking accordingly.
> 
> Hugh Dickins pointed that __page_cache_release and release_pages
> has no need to do atomic clear bit since no user on the page at that
> moment. and no need get_page() before lru bit clear in isolate_lru_page,
> since it '(1) Must be called with an elevated refcount on the page'.
> 
> As Andrew Morton mentioned this change would dirty cacheline for page
> isn't on LRU. But the lost would be acceptable with Rong Chen
> <rong.a.chen@intel.com> report:
> https://lkml.org/lkml/2020/3/4/173
> 
> Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
> Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: linux-kernel@vger.kernel.org
> Cc: cgroups@vger.kernel.org
> Cc: linux-mm@kvack.org
> ---
>  include/linux/page-flags.h |  1 +
>  mm/mlock.c                 |  3 +--
>  mm/swap.c                  |  6 ++----
>  mm/vmscan.c                | 26 +++++++++++---------------
>  4 files changed, 15 insertions(+), 21 deletions(-)
> 
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 6be1aa559b1e..9554ed1387dc 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -326,6 +326,7 @@ static inline void page_init_poison(struct page *page, size_t size)
>  PAGEFLAG(Dirty, dirty, PF_HEAD) TESTSCFLAG(Dirty, dirty, PF_HEAD)
>  	__CLEARPAGEFLAG(Dirty, dirty, PF_HEAD)
>  PAGEFLAG(LRU, lru, PF_HEAD) __CLEARPAGEFLAG(LRU, lru, PF_HEAD)
> +	TESTCLEARFLAG(LRU, lru, PF_HEAD)
>  PAGEFLAG(Active, active, PF_HEAD) __CLEARPAGEFLAG(Active, active, PF_HEAD)
>  	TESTCLEARFLAG(Active, active, PF_HEAD)
>  PAGEFLAG(Workingset, workingset, PF_HEAD)
> diff --git a/mm/mlock.c b/mm/mlock.c
> index f8736136fad7..228ba5a8e0a5 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -108,13 +108,12 @@ void mlock_vma_page(struct page *page)
>   */
>  static bool __munlock_isolate_lru_page(struct page *page, bool getpage)
>  {
> -	if (PageLRU(page)) {
> +	if (TestClearPageLRU(page)) {
>  		struct lruvec *lruvec;
>  
>  		lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page));
>  		if (getpage)
>  			get_page(page);
> -		ClearPageLRU(page);
>  		del_page_from_lru_list(page, lruvec, page_lru(page));
>  		return true;
>  	}
> diff --git a/mm/swap.c b/mm/swap.c
> index f645965fde0e..5092fe9c8c47 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -83,10 +83,9 @@ static void __page_cache_release(struct page *page)
>  		struct lruvec *lruvec;
>  		unsigned long flags;
>  
> +		__ClearPageLRU(page);
>  		spin_lock_irqsave(&pgdat->lru_lock, flags);
>  		lruvec = mem_cgroup_page_lruvec(page, pgdat);
> -		VM_BUG_ON_PAGE(!PageLRU(page), page);
> -		__ClearPageLRU(page);
>  		del_page_from_lru_list(page, lruvec, page_off_lru(page));
>  		spin_unlock_irqrestore(&pgdat->lru_lock, flags);
>  	}
> @@ -878,9 +877,8 @@ void release_pages(struct page **pages, int nr)
>  				spin_lock_irqsave(&locked_pgdat->lru_lock, flags);
>  			}
>  
> -			lruvec = mem_cgroup_page_lruvec(page, locked_pgdat);
> -			VM_BUG_ON_PAGE(!PageLRU(page), page);
>  			__ClearPageLRU(page);
> +			lruvec = mem_cgroup_page_lruvec(page, locked_pgdat);
>  			del_page_from_lru_list(page, lruvec, page_off_lru(page));
>  		}
>  
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index c1c4259b4de5..18986fefd49b 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1548,16 +1548,16 @@ int __isolate_lru_page(struct page *page, isolate_mode_t mode)
>  {
>  	int ret = -EINVAL;
>  
> -	/* Only take pages on the LRU. */
> -	if (!PageLRU(page))
> -		return ret;
> -
>  	/* Compaction should not handle unevictable pages but CMA can do so */
>  	if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
>  		return ret;
>  
>  	ret = -EBUSY;
>  
> +	/* Only take pages on the LRU. */
> +	if (!PageLRU(page))
> +		return ret;
> +
>  	/*
>  	 * To minimise LRU disruption, the caller can indicate that it only
>  	 * wants to isolate pages it will be able to operate on without
> @@ -1671,8 +1671,6 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
>  		page = lru_to_page(src);
>  		prefetchw_prev_lru_page(page, src, flags);
>  
> -		VM_BUG_ON_PAGE(!PageLRU(page), page);
> -
>  		nr_pages = compound_nr(page);
>  		total_scan += nr_pages;
>  
> @@ -1769,21 +1767,19 @@ int isolate_lru_page(struct page *page)
>  	VM_BUG_ON_PAGE(!page_count(page), page);
>  	WARN_RATELIMIT(PageTail(page), "trying to isolate tail page");
>  
> -	if (PageLRU(page)) {
> +	if (TestClearPageLRU(page)) {
>  		pg_data_t *pgdat = page_pgdat(page);
>  		struct lruvec *lruvec;
> +		int lru = page_lru(page);
>  
> -		spin_lock_irq(&pgdat->lru_lock);
> +		get_page(page);
>  		lruvec = mem_cgroup_page_lruvec(page, pgdat);
> -		if (PageLRU(page)) {
> -			int lru = page_lru(page);
> -			get_page(page);
> -			ClearPageLRU(page);
> -			del_page_from_lru_list(page, lruvec, lru);
> -			ret = 0;
> -		}
> +		spin_lock_irq(&pgdat->lru_lock);
> +		del_page_from_lru_list(page, lruvec, lru);
>  		spin_unlock_irq(&pgdat->lru_lock);
> +		ret = 0;
>  	}
> +
>  	return ret;
>  }
>  
>