On Mon, Feb 22, 2021 at 12:42:46PM +0100, Jesper Dangaard Brouer wrote: > 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'm waiting to find out exactly what NFSD is currently doing as the code in 5.11 is not the same as what Chuck was coding against so I'm not 100% certain how it currently works. > > > 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() ? > There isn't a usable latest version until I reconcile the nfsd caller. The only major change in the API right now is dropping order. It handles order-0 only. -- Mel Gorman SUSE Labs
