在 2020/4/16 下午11:28, Johannes Weiner 写道: > Hi Alex, > > On Thu, Apr 16, 2020 at 04:01:20PM +0800, Alex Shi wrote: >> >> >> 在 2020/4/15 下午9:42, Alex Shi 写道: >>> Hi Johannes, >>> >>> Thanks a lot for point out! >>> >>> Charging in __read_swap_cache_async would ask for 3 layers function arguments >>> pass, that would be a bit ugly. Compare to this, could we move out the >>> lru_cache add after commit_charge, like ksm copied pages? >>> >>> That give a bit extra non lru list time, but the page just only be used only >>> after add_anon_rmap setting. Could it cause troubles? >> >> Hi Johannes & Andrew, >> >> Doing lru_cache_add_anon during swapin_readahead can give a very short timing >> for possible page reclaiming for these few pages. >> >> If we delay these few pages lru adding till after the vm_fault target page >> get memcg charging(mem_cgroup_commit_charge) and activate, we could skip the >> mem_cgroup_try_charge/commit_charge/cancel_charge process in __read_swap_cache_async(). >> But the cost is maximum SWAP_RA_ORDER_CEILING number pages on each cpu miss >> page reclaiming in a short time. On the other hand, save the target vm_fault >> page from reclaiming before activate it during that time. > > The readahead pages surrounding the faulting page might never get > accessed and pile up to large amounts. Users can also trigger > non-faulting readahead with MADV_WILLNEED. > > So unfortunately, I don't see a way to keep these pages off the > LRU. They do need to be reclaimable, or they become a DoS vector. > > I'm currently preparing a small patch series to make swap ownership > tracking an integral part of memcg and change the swapin charging > sequence, then you don't have to worry about it. This will also > unblock Joonsoo's "workingset protection/detection on the anonymous > LRU list" patch series, since he is blocked on the same problem - he > needs the correct LRU available at swapin time to process refaults > correctly. Both of your patch series are already pretty large, they > shouldn't need to also deal with that. > That sounds great! BTW, the swapin target page will add into inactive_anon list and then activate after chaged. that left a minum time slot for this page to be reclaimed. May better activate it early? Also I have 2 clean up patches, which may or may not useful for you. will send it to you. :) Thanks Alex
