On Mon, 22 Feb 2021 09:42:56 +0000 Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> wrote: > On Mon, Feb 15, 2021 at 05:10:38PM +0100, Jesper Dangaard Brouer wrote: > > > > On Mon, 15 Feb 2021 12:00:56 +0000 > > Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > On Thu, Feb 11, 2021 at 01:26:28PM +0100, Jesper Dangaard Brouer wrote: > > [...] > > > > > > > I also suggest the API can return less pages than requested. Because I > > > > want to to "exit"/return if it need to go into an expensive code path > > > > (like buddy allocator or compaction). I'm assuming we have a flags to > > > > give us this behavior (via gfp_flags or alloc_flags)? > > > > > > > > > > The API returns the number of pages returned on a list so policies > > > around how aggressive it should be allocating the requested number of > > > pages could be adjusted without changing the API. Passing in policy > > > requests via gfp_flags may be problematic as most (all?) bits are > > > already used. > > > > Well, I was just thinking that I would use GFP_ATOMIC instead of > > GFP_KERNEL to "communicate" that I don't want this call to take too > > long (like sleeping). I'm not requesting any fancy policy :-) > > > > The NFS use case requires opposite semantics > -- it really needs those allocations to succeed > https://lore.kernel.org/r/161340498400.7780.962495219428962117.stgit@xxxxxxxxxxxxxxxxxxxxx. Sorry, but that is not how I understand the code. The code is doing exactly what I'm requesting. If the alloc_pages_bulk() doesn't return expected number of pages, then check if others need to run. The old code did schedule_timeout(msecs_to_jiffies(500)), while Chuck's patch change this to ask for cond_resched(). Thus, it tries to avoid blocking the CPU for too long (when allocating many pages). And the nfsd code seems to handle that the code can be interrupted (via return -EINTR) via signal_pending(current). Thus, the nfsd code seems to be able to handle if the page allocations failed. > I've asked what code it's based on as it's not 5.11 and I'll iron that > out first. > > Then it might be clearer what the "can fail" semantics should look like. > I think it would be best to have pairs of patches where the first patch > adjusts the semantics of the bulk allocator and the second adds a user. > That will limit the amount of code code carried in the implementation. > When the initial users are in place then the implementation can be > optimised as the optimisations will require significant refactoring and > I not want to refactor multiple times. I guess, I should try to code-up the usage in page_pool. What is the latest patch for adding alloc_pages_bulk() ? The nfsd code (svc_alloc_arg) is called in a context where it can sleep, and thus use GFP_KERNEL. In most cases the page_pool will be called with GFP_ATOMIC. I don't think I/page_pool will retry the call like Chuck did, as I cannot (re)schedule others to run. -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
