在 2023/3/20 17:12, Mike Rapoport 写道: > On Mon, Mar 20, 2023 at 09:05:57AM +0100, Vlastimil Babka wrote: >> On 3/19/23 08:22, chenjun (AM) wrote: >>> 在 2023/3/17 20:06, Vlastimil Babka 写道: >>>> On 3/17/23 12:32, chenjun (AM) wrote: >>>>> 在 2023/3/14 22:41, Vlastimil Babka 写道: >>>>>>> pc.flags = gfpflags; >>>>>>> + >>>>>>> + /* >>>>>>> + * when (node != NUMA_NO_NODE) && (gfpflags & __GFP_THISNODE) >>>>>>> + * 1) try to get a partial slab from target node with __GFP_THISNODE. >>>>>>> + * 2) if 1) failed, try to allocate a new slab from target node with >>>>>>> + * __GFP_THISNODE. >>>>>>> + * 3) if 2) failed, retry 1) and 2) without __GFP_THISNODE constraint. >>>>>>> + */ >>>>>>> + if (node != NUMA_NO_NODE && !(gfpflags & __GFP_THISNODE) && try_thisnode) >>>>>>> + pc.flags |= __GFP_THISNODE; >>>>>> >>>>>> Hmm I'm thinking we should also perhaps remove direct reclaim possibilities >>>>>> from the attempt 2). In your qemu test it should make no difference, as it >>>>>> fills everything with kernel memory that is not reclaimable. But in practice >>>>>> the target node might be filled with user memory, and I think it's better to >>>>>> quickly allocate on a different node than spend time in direct reclaim. So >>>>>> the following should work I think? >>>>>> >>>>>> pc.flags = GFP_NOWAIT | __GFP_NOWARN |__GFP_THISNODE >>>>>> >>>>> >>>>> Hmm, Should it be that: >>>>> >>>>> pc.flags |= GFP_NOWAIT | __GFP_NOWARN |__GFP_THISNODE >>>> >>>> No, we need to ignore the other reclaim-related flags that the caller >>>> passed, or it wouldn't work as intended. >>>> The danger is that we ignore some flag that would be necessary to pass, but >>>> I don't think there's any? >>>> >>>> >>> >>> If we ignore __GFP_ZERO passed by kzalloc， kzalloc will not work. >>> Could we just unmask __GFP_RECLAIMABLE | __GFP_RECLAIM? >>> >>> pc.flags &= ~(__GFP_RECLAIMABLE | __GFP_RECLAIM) >>> pc.flags |= __GFP_THISNODE >> >> __GFP_RECLAIMABLE would be wrong, but also ignored as new_slab() does: >> flags & (GFP_RECLAIM_MASK | GFP_CONSTRAINT_MASK) >> >> which would filter out __GFP_ZERO as well. That's not a problem as kzalloc() >> will zero out the individual allocated objects, so it doesn't matter if we >> don't zero out the whole slab page. >> >> But I wonder, if we're not past due time for a helper e.g. >> gfp_opportunistic(flags) that would turn any allocation flags to a >> GFP_NOWAIT while keeping the rest of relevant flags intact, and thus there >> would be one canonical way to do it - I'm sure there's a number of places >> with their own variants now? >> With such helper we'd just add __GFP_THISNODE to the result here as that's >> specific to this particular opportunistic allocation. > > I like the idea, but maybe gfp_no_reclaim() would be clearer? > #define gfp_no_reclaim(gfpflag) (gfpflag & ~__GFP_DIRECT_RECLAIM) And here, pc.flags = gfp_no_reclaim(gfpflags) | __GFP_THISNODE. Do I get it right？
