On 6/17/20 7:26 AM, js1304@xxxxxxxxx wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Hi, how about a more descriptive subject, such as
mm/vmscan: add new anonymous pages to inactive LRU list
> In current implementation, newly created or swap-in anonymous page
> is started on active list. Growing active list results in rebalancing
> active/inactive list so old pages on active list are demoted to inactive
> list. Hence, the page on active list isn't protected at all.
>
> Following is an example of this situation.
>
> Assume that 50 hot pages on active list. Numbers denote the number of
> pages on active/inactive list (active | inactive).
>
> 1. 50 hot pages on active list
> 50(h) | 0
>
> 2. workload: 50 newly created (used-once) pages
> 50(uo) | 50(h)
>
> 3. workload: another 50 newly created (used-once) pages
> 50(uo) | 50(uo), swap-out 50(h)
>
> This patch tries to fix this issue.
> Like as file LRU, newly created or swap-in anonymous pages will be
> inserted to the inactive list. They are promoted to active list if
> enough reference happens. This simple modification changes the above
> example as following.
>
> 1. 50 hot pages on active list
> 50(h) | 0
>
> 2. workload: 50 newly created (used-once) pages
> 50(h) | 50(uo)
>
> 3. workload: another 50 newly created (used-once) pages
> 50(h) | 50(uo), swap-out 50(uo)
>
> As you can see, hot pages on active list would be protected.
>
> Note that, this implementation has a drawback that the page cannot
> be promoted and will be swapped-out if re-access interval is greater than
> the size of inactive list but less than the size of total(active+inactive).
> To solve this potential issue, following patch will apply workingset
> detection that is applied to file LRU some day before.
detection similar to the one that's already applied to file LRU.
> v6: Before this patch, all anon pages (inactive + active) are considered
> as workingset. However, with this patch, only active pages are considered
> as workingset. So, file refault formula which uses the number of all
> anon pages is changed to use only the number of active anon pages.
a "v6" note is more suitable for a diffstat area than commit log, but it's good
to mention this so drop the 'v6:'?
> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
One more nit below.
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -476,23 +476,24 @@ void lru_cache_add(struct page *page)
> EXPORT_SYMBOL(lru_cache_add);
>
> /**
> - * lru_cache_add_active_or_unevictable
> + * lru_cache_add_inactive_or_unevictable
> * @page: the page to be added to LRU
> * @vma: vma in which page is mapped for determining reclaimability
> *
> - * Place @page on the active or unevictable LRU list, depending on its
> + * Place @page on the inactive or unevictable LRU list, depending on its
> * evictability. Note that if the page is not evictable, it goes
> * directly back onto it's zone's unevictable list, it does NOT use a
> * per cpu pagevec.
> */
> -void lru_cache_add_active_or_unevictable(struct page *page,
> +void lru_cache_add_inactive_or_unevictable(struct page *page,
> struct vm_area_struct *vma)
> {
> + bool unevictable;
> +
> VM_BUG_ON_PAGE(PageLRU(page), page);
>
> - if (likely((vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) != VM_LOCKED))
> - SetPageActive(page);
> - else if (!TestSetPageMlocked(page)) {
> + unevictable = (vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) == VM_LOCKED;
> + if (unevictable && !TestSetPageMlocked(page)) {
I guess this could be "if (unlikely(unevictable) && ..." to match the previous
if (likely(evictable)) else ...
> /*
> * We use the irq-unsafe __mod_zone_page_stat because this
> * counter is not modified from interrupt context, and the pte
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index c047789..38f6433 100644
