Re: [PATCH v9 16/17] mm: make vma cache SLAB_TYPESAFE_BY_RCU

[Wei Yang]

On Tue, Jan 14, 2025 at 07:15:05PM -0800, Suren Baghdasaryan wrote:
>On Tue, Jan 14, 2025 at 6:27 PM Wei Yang <richard.weiyang@xxxxxxxxx> wrote:
>>
>> On Fri, Jan 10, 2025 at 08:26:03PM -0800, Suren Baghdasaryan wrote:
>>
>> >diff --git a/kernel/fork.c b/kernel/fork.c
>> >index 9d9275783cf8..151b40627c14 100644
>> >--- a/kernel/fork.c
>> >+++ b/kernel/fork.c
>> >@@ -449,6 +449,42 @@ struct vm_area_struct *vm_area_alloc(struct mm_struct *mm)
>> >       return vma;
>> > }
>> >
>> >+static void vm_area_init_from(const struct vm_area_struct *src,
>> >+                            struct vm_area_struct *dest)
>> >+{
>> >+      dest->vm_mm = src->vm_mm;
>> >+      dest->vm_ops = src->vm_ops;
>> >+      dest->vm_start = src->vm_start;
>> >+      dest->vm_end = src->vm_end;
>> >+      dest->anon_vma = src->anon_vma;
>> >+      dest->vm_pgoff = src->vm_pgoff;
>> >+      dest->vm_file = src->vm_file;
>> >+      dest->vm_private_data = src->vm_private_data;
>> >+      vm_flags_init(dest, src->vm_flags);
>> >+      memcpy(&dest->vm_page_prot, &src->vm_page_prot,
>> >+             sizeof(dest->vm_page_prot));
>> >+      /*
>> >+       * src->shared.rb may be modified concurrently when called from
>> >+       * dup_mmap(), but the clone will reinitialize it.
>> >+       */
>> >+      data_race(memcpy(&dest->shared, &src->shared, sizeof(dest->shared)));
>> >+      memcpy(&dest->vm_userfaultfd_ctx, &src->vm_userfaultfd_ctx,
>> >+             sizeof(dest->vm_userfaultfd_ctx));
>> >+#ifdef CONFIG_ANON_VMA_NAME
>> >+      dest->anon_name = src->anon_name;
>> >+#endif
>> >+#ifdef CONFIG_SWAP
>> >+      memcpy(&dest->swap_readahead_info, &src->swap_readahead_info,
>> >+             sizeof(dest->swap_readahead_info));
>> >+#endif
>> >+#ifndef CONFIG_MMU
>> >+      dest->vm_region = src->vm_region;
>> >+#endif
>> >+#ifdef CONFIG_NUMA
>> >+      dest->vm_policy = src->vm_policy;
>> >+#endif
>> >+}
>>
>> Would this be difficult to maintain? We should make sure not miss or overwrite
>> anything.
>
>Yeah, it is less maintainable than a simple memcpy() but I did not
>find a better alternative. I added a warning above the struct
>vm_area_struct definition to update this function every time we change
>that structure. Not sure if there is anything else I can do to help
>with this.
>

For !PER_VMA_LOCK, maybe we can use memcpy() as usual.

For PER_VMA_LOCK, I just come up the same idea with you:-)

>>
>> --
>> Wei Yang
>> Help you, Help me

-- 
Wei Yang
Help you, Help me