On Wed, May 01, 2019 at 11:21:08AM -0400, Doug Ledford wrote: > On Mar 27, 2019, at 1:02 PM, Leon Romanovsky <leon@xxxxxxxxxx> wrote: > > > > On Wed, Mar 27, 2019 at 08:25:17AM -0700, Tejun Heo (tj@xxxxxxxxxx) wrote: > >> Hello, > >> > >> On Tue, Mar 26, 2019 at 08:55:09PM +0000, Marciniszyn, Mike wrote: > >>> The latter is the ipoib wq that conflicts with our non-WQ_MEM_RECLAIM. This seems excessive and pretty gratuitous. > >>> > >>> Tejun, what does "mem reclaim" really mean and when should it be used? > >> > >> That it may be depended during memory reclaim. > >> > >>> I was assuming that since we are freeing QP kernel memory held by user mode programs that could be oom killed, we need the flag. > >> > >> If it can't block memory reclaim, it doesn't need the flag. Just in > >> case, if a workqueue is used to issue block IOs, it is depended upon > >> for memory reclaim as writeback and swap-outs are critical parts of > >> memory reclaim. > > > > It looks like WQ_MEM_RECLAIM is needed for IPoIB, because if NFS runs > > over IPoIB, it will do those types of IOs. > > Because of what IPoIB does, you’re right that it’s needed. However, > it might be necessary to audit the wq usage in IPoIB to make sure > it’s actually eligible for the flag and that it hasn’t been set when > the code doesn’t meet the requirements of the flag. It isn't right - it is doing memory allocations from the work queue without the GFP_NOIO (or memalloc_noio_save) And I'm not sure it can actually tolerate failure of a memory allocation anyhow without blocking the dataplane. In other words, the entire thing hasn't been designed with the idea that it could be on the IO path.. I'm not sure how things work if NFS is on the critical reclaim path in general - does it even work with a normal netdev? How does netdev allocate a neighbor for instance if it becomes required? Jason
