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.
