Re: [PATCH 16/18] mm: memcontrol: charge swapin pages on instantiation

[Alex Shi]

在 2020/4/21 上午6:11, Johannes Weiner 写道:
> Right now, users that are otherwise memory controlled can easily
> escape their containment and allocate significant amounts of memory
> that they're not being charged for. That's because swap readahead
> pages are not being charged until somebody actually faults them into
> their page table. This can be exploited with MADV_WILLNEED, which
> triggers arbitrary readahead allocations without charging the pages.
> 
> There are additional problems with the delayed charging of swap pages:
> 
> 1. To implement refault/workingset detection for anonymous pages, we
>    need to have a target LRU available at swapin time, but the LRU is
>    not determinable until the page has been charged.
> 
> 2. To implement per-cgroup LRU locking, we need page->mem_cgroup to be
>    stable when the page is isolated from the LRU; otherwise, the locks
>    change under us. But swapcache gets charged after it's already on
>    the LRU, and even if we cannot isolate it ourselves (since charging
>    is not exactly optional).
> 
> The previous patch ensured we always maintain cgroup ownership records
> for swap pages. This patch moves the swapcache charging point from the
> fault handler to swapin time to fix all of the above problems.
> 
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Reviewed-by: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>