Re: [PATCH] xfs: Remove kmem_zalloc_large()

[Dave Chinner <david@fromorbit.com>]

On Tue, Aug 25, 2020 at 04:34:58PM +0200, Carlos Maiolino wrote:
> This patch aims to replace kmem_zalloc_large() with global kernel memory
> API. So, all its callers are now using kvzalloc() directly, so kmalloc()
> fallsback to vmalloc() automatically.
> 
> __GFP_RETRY_MAYFAIL has been set because according to memory documentation,
> it should be used in case kmalloc() is preferred over vmalloc().
> 
> Patch survives xfstests with large (32GiB) and small (4GiB) RAM memory amounts.
> 
> Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
> ---
>  fs/xfs/kmem.h          | 6 ------
>  fs/xfs/scrub/symlink.c | 4 +++-
>  fs/xfs/xfs_acl.c       | 3 ++-
>  fs/xfs/xfs_ioctl.c     | 5 +++--
>  fs/xfs/xfs_rtalloc.c   | 3 ++-
>  5 files changed, 10 insertions(+), 11 deletions(-)
> 
> I'm not entirely sure passing __GFP_RETRY_MAYFAIL is the right thing to do here,
> but since current api attempts a kmalloc before falling back to vmalloc, it
> seems to be correct to pass it.

I don't think __GFP_RETRY_MAYFAIL is necessary. If the allocation is
larger than ALLOC_ORDER_COSTLY (8 pages, I think) then kmalloc()
will fail rather than retry forever and then it falls back to
vmalloc. Hence I don't think we need to tell the kmalloc() it needs
to fail large allocations if it can't make progress...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com