Re: [PATCH v4 1/3] btrfs: add might_sleep() to some places in update_qgroup_limit_item()

[Qu Wenruo]

On 2022/11/16 16:09, ChenXiaoSong wrote:
> 在 2022/11/16 6:48, Qu Wenruo 写道:
> > Looks good.
> >
> > We may want to add more in other locations, but this is really a good 
> > start.
> >
> > Reviewed-by: Qu Wenruo <wqu@xxxxxxxx>
> >
> > Thanks,
> > Qu
>
> If I just add might_sleep() in btrfs_alloc_path() and 
> btrfs_search_slot(), is it reasonable?

Adding it to btrfs_search_slot() is definitely correct.

But why for btrfs_alloc_path()? Wouldn't kmem_cache_zalloc() itself 
already do the might_sleep_if() somewhere?

I just looked the call chain, and indeed it is doing the check already:

btrfs_alloc_path()
|- kmem_cache_zalloc()
   |- kmem_cache_alloc()
      |- __kmem_cache_alloc_lru()
         |- slab_alloc()
            |- slab_alloc_node()
               |- slab_pre_alloc_hook()
                  |- might_alloc()
                     |- might_sleep_if()

Thanks,
Qu

> Or just add might_sleep() to one place in update_qgroup_limit_item() ?