On Tue, Mar 17, 2020 at 02:41:50PM +0900, js1304@xxxxxxxxx wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
>
> 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.
>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> -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 evictable;
> +
> VM_BUG_ON_PAGE(PageLRU(page), page);
>
> - if (likely((vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) != VM_LOCKED))
> - SetPageActive(page);
> - else if (!TestSetPageMlocked(page)) {
> + evictable = (vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) != VM_LOCKED;
> + if (!evictable && !TestSetPageMlocked(page)) {
Minor point, but in case there is a v4: `unevictable` instead of
!evictable would be a bit easier to read, match the function name,
PageUnevictable etc.
