On Tue 02-05-23 09:45:40, Vlastimil Babka wrote: > On 5/1/23 20:58, Mike Kravetz wrote: > > I received a question from a customer that was trying to move pages via > > the mbind system call. In this specific case, the system had two nodes > > and all pages in the range were already present on node 0. They then > > called mbind with mode MPOL_INTERLEAVE and the MPOL_MF_MOVE_ALL flag. Their > > expectation was that half the pages in the range would be moved to node 1 > > in an interleaved pattern. > > > > In the above situation, no pages actually get moved. This is because mbind > > creates a list of pages to be moved via: > > > > ret = queue_pages_range(mm, start, end, nmask, > > flags | MPOL_MF_INVERT, &pagelist); > > > > No page will be added to the list as queue_folio_required is called for each > > page to determine if it resides within the set of nodes. And, all page are > > within the set. > > > > I have reread the mbind man page several times and agree that one might > > expect MPOL_INTERLEAVE with MPOL_MF_MOVE_ALL to move pages and create an > > interleaved pattern. My question is should we: > > - Change mbind so that pages are moved to an interleaved pattern? > > I guess it could be worth trying, if there's a use case. And hope nobody > else is depending on the current behavior and will complain afterwards :) I am not sure this is worth it wrt. complexity. Essentially it would require to build up the distribution for the whole range first so 2 passes. Also it could become more tricky if the final node mask has nodes of difference distances (it would be a reasonable expectation to distribute withe minimum total distances right ;)). > > - Update the documentation to be more explicit? Yes, please. I do not think. While this sounds like a neat feature I think the additional complexity is likely not worth it. A strong usecase might make a difference though. -- Michal Hocko SUSE Labs
