On Tue, 29 Apr 2025, cel@xxxxxxxxxx wrote: > From: Chuck Lever <chuck.lever@xxxxxxxxxx> > > In order to make RPCSVC_MAXPAYLOAD larger (or variable in size), we > need to do something clever with the payload arrays embedded in > struct svc_rqst and elsewhere. > > My preference is to keep these arrays allocated all the time because > allocating them on demand increases the risk of a memory allocation > failure during a large I/O. This is a quick-and-dirty approach that > might be replaced once NFSD is converted to use large folios. > > The downside of this design choice is that it pins a few pages per > NFSD thread (and that's the current situation already). But note > that because RPCSVC_MAXPAGES is 259, each array is just over a page > in size, making the allocation waste quite a bit of memory beyond > the end of the array due to power-of-2 allocator round up. This gets > worse as the MAXPAGES value is doubled or quadrupled. I wonder if we should special-case those 3 extra. We don't need any for rq_vec and only need 2 (I think) for rq_bvec. We could use the arrays only for payload and have dedicated page/vec/bvec for request, reply, read-padding. Or maybe we could not allow read requests that result in the extra page due to alignment needs. Would that be much cost? Apart from the one issue I noted separately, I think the series looks good. Reviewed-by: NeilBrown <neil@xxxxxxxxxx> Thanks, NeilBrown
