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? -- Sincerely yours, Mike.
