Re: [PATCH v1] mm/mm_init: Fix hash table order logging in alloc_large_system_hash()

[Isaac Manjarres <isaacmanjarres@google.com>]

On Wed, Oct 29, 2025 at 11:03:18AM +0100, David Hildenbrand wrote:
> On 28.10.25 20:10, Isaac J. Manjarres wrote:
> > When emitting the order of the allocation for a hash table,
> > alloc_large_system_hash() unconditionally subtracts PAGE_SHIFT from
> > log base 2 of the allocation size. This is not correct if the
> > allocation size is smaller than a page, and yields a negative value
> > for the order as seen below:
> > 
> > TCP established hash table entries: 32 (order: -4, 256 bytes, linear)
> > TCP bind hash table entries: 32 (order: -2, 1024 bytes, linear)
> > 
> > Use get_order() to compute the order when emitting the hash table
> > information to correctly handle cases where the allocation size is
> > smaller than a page:
> > 
> > TCP established hash table entries: 32 (order: 0, 256 bytes, linear)
> > TCP bind hash table entries: 32 (order: 0, 1024 bytes, linear)
> > 
> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > Cc: stable@vger.kernel.org # v5.4+
> 
> This is a pr_info(), why do you think this is stable material? Just curious,
> intuitively I'd have said that it's not that critical.
> 

Hi David,

Thank you for taking the time to review this patch! I was just under the
impression that any bug--even those for informational logging--should be
sent to stable as well.

> > Signed-off-by: Isaac J. Manjarres <isaacmanjarres@google.com>
> > ---
> >   mm/mm_init.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/mm/mm_init.c b/mm/mm_init.c
> > index 3db2dea7db4c..7712d887b696 100644
> > --- a/mm/mm_init.c
> > +++ b/mm/mm_init.c
> > @@ -2469,7 +2469,7 @@ void *__init alloc_large_system_hash(const char *tablename,
> >   		panic("Failed to allocate %s hash table\n", tablename);
> >   	pr_info("%s hash table entries: %ld (order: %d, %lu bytes, %s)\n",
> > -		tablename, 1UL << log2qty, ilog2(size) - PAGE_SHIFT, size,
> > +		tablename, 1UL << log2qty, get_order(size), size,
> 
> So in case it's smaller than a page we now correctly return "0".

Correct.

> Reviewed-by: David Hildenbrand <david@redhat.com>
> 
> -- 
> Cheers
> 
> David / dhildenb

Thanks!
Isaac