On 2019/09/11 22:52, Hillf Danton wrote: > > On Wed, 11 Sep 2019 19:07:34 +0900 >> >> But I guess that there is a problem. > > Not a new one. (see commit 7dea19f9ee63) > >> Setting PF_MEMALLOC_NOIO causes >> current_gfp_context() to mask __GFP_IO | __GFP_FS, but the OOM killer cannot >> be invoked when __GFP_FS is masked. As a result, any userspace thread which >> has PF_MEMALLOC_NOIO cannot invoke the OOM killer. > > Correct. > >> If the userspace thread >> which uses PF_MEMALLOC_NOIO is involved in memory reclaiming activities, >> the memory reclaiming activities won't be able to make forward progress when >> the userspace thread triggered e.g. a page fault. Can the "userspace components >> that can run in the IO path" survive without any memory allocation? > > Good question. > > It can be solved without oom killer involved because user should be > aware of the risk of PF_MEMALLOC_NOIO if they ask for the convenience. > OTOH we are able to control any abuse of it as you worry, knowing that > the combination of __GFP_FS and oom killer can not get more than 50 users > works done, and we have to pay as much attention as we can to the decisions > they make. In case of PF_MEMALLOC_NOIO, we simply fail the allocation > rather than killing a random victim. According to commit c288983dddf71421 ("mm/page_alloc.c: make sure OOM victim can try allocations with no watermarks once"), memory allocation failure from a page fault results in invocation of the OOM killer via pagefault_out_of_memory() which after all kills a random victim. > > > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3854,6 +3854,8 @@ __alloc_pages_may_oom(gfp_t gfp_mask, un > * out_of_memory). Once filesystems are ready to handle allocation > * failures more gracefully we should just bail out here. > */ > + if (current->flags & PF_MEMALLOC_NOIO) > + goto out; > > /* The OOM killer may not free memory on a specific node */ > if (gfp_mask & __GFP_THISNODE) > >