Messages in this thread | | | Subject | Re: [PATCH 3/5] mm: Rework return value for copy_one_pte() | From | John Hubbard <> | Date | Tue, 22 Sep 2020 00:11:29 -0700 |
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On 9/21/20 2:17 PM, Peter Xu wrote: > There's one special path for copy_one_pte() with swap entries, in which > add_swap_count_continuation(GFP_ATOMIC) might fail. In that case we'll return
I might be looking at the wrong place, but the existing code seems to call add_swap_count_continuation(GFP_KERNEL), not with GFP_ATOMIC?
> the swp_entry_t so that the caller will release the locks and redo the same > thing with GFP_KERNEL. > > It's confusing when copy_one_pte() must return a swp_entry_t (even if all the > ptes are non-swap entries). More importantly, we face other requirement to > extend this "we need to do something else, but without the locks held" case. > > Rework the return value into something easier to understand, as defined in enum > copy_mm_ret. We'll pass the swp_entry_t back using the newly introduced union
I like the documentation here, but it doesn't match what you did in the patch. Actually, the documentation had the right idea (enum, rather than #define, for COPY_MM_* items). Below...
> copy_mm_data parameter. > > Another trivial change is to move the reset of the "progress" counter into the > retry path, so that we'll reset it for other reasons too. > > This should prepare us with adding new return codes, very soon. > > Signed-off-by: Peter Xu <peterx@redhat.com> > --- > mm/memory.c | 42 +++++++++++++++++++++++++++++------------- > 1 file changed, 29 insertions(+), 13 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 7525147908c4..1530bb1070f4 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -689,16 +689,24 @@ struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr, > } > #endif > > +#define COPY_MM_DONE 0 > +#define COPY_MM_SWAP_CONT 1
Those should be enums, so as to get a little type safety and other goodness from using non-macro items.
... > @@ -866,13 +877,18 @@ static int copy_pte_range(struct mm_struct *dst_mm, struct mm_struct *src_mm, > pte_unmap_unlock(orig_dst_pte, dst_ptl); > cond_resched(); > > - if (entry.val) { > - if (add_swap_count_continuation(entry, GFP_KERNEL) < 0) > + switch (copy_ret) { > + case COPY_MM_SWAP_CONT: > + if (add_swap_count_continuation(data.entry, GFP_KERNEL) < 0) > return -ENOMEM; > - progress = 0;
Yes. Definitely a little cleaner to reset this above, instead of here.
> + break; > + default: > + break;
I assume this no-op noise is to placate the compiler and/or static checkers. :)
I'm unable to find any actual problems with the diffs, aside from the nit about using an enum.
thanks, -- John Hubbard NVIDIA
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