Re: [PATCH v2 08/16] mm/slab: pass alloc_flags to new slab allocation

[Harry Yoo <harry@kernel.org>]

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On 6/11/26 12:40 AM, Vlastimil Babka (SUSE) wrote:
> Add the alloc_flags parameter to allocate_slab() and new_slab()
> so it can be used to determine if spinning is allowed, independently
> from gfp flags.
> 
> refill_objects() passes SLAB_ALLOC_DEFAULT because it can only be
> reached from contexts that allow spinning.
> 
> Also change how trynode_flags are constructed in ___slab_alloc() to
> achieve the same "do not upgrade to GFP_NOWAIT" by using masking instead
> of a branch. It will now also not upgrade in cases where gfp is weaker
> than GFP_NOWAIT (i.e. lacks __GFP_KSWAPD_RECLAIM) but doesn't come from
> kmalloc_nolock() - which is more correct anyway.

Wait, debugobjects intentionally avoids __GFP_KSWAPD_RECLAIM,
but we have been upgrading it to GFP_NOWAIT?

> During the masking keep also existing __GFP_NOMEMALLOC (pointed out by
> Sashiko) and __GFP_ACCOUNT. Previously the hardcoded GFP_NOWAIT would
> eliminate them, but it's not a big problem that would need a separate
> fix.

Ack.

> Signed-off-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
> ---
>  mm/slub.c | 28 ++++++++++++++--------------
>  1 file changed, 14 insertions(+), 14 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index 98b79e5e7679..8f6ca3d5fdfa 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -4467,25 +4470,22 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
>  	 * 1) try to get a partial slab from target node only by having
>  	 *    __GFP_THISNODE in pc.flags for get_from_partial()
>  	 * 2) if 1) failed, try to allocate a new slab from target node with
> -	 *    GPF_NOWAIT | __GFP_THISNODE opportunistically
> +	 *    (at most) GFP_NOWAIT | __GFP_THISNODE opportunistically
>  	 * 3) if 2) failed, retry with original gfpflags which will allow
>  	 *    get_from_partial() try partial lists of other nodes before
>  	 *    potentially allocating new page from other nodes
>  	 */
>  	if (unlikely(node != NUMA_NO_NODE && !(gfpflags & __GFP_THISNODE)
>  		     && try_thisnode)) {
> -		if (unlikely(!allow_spin))
> -			/* Do not upgrade gfp to NOWAIT from more restrictive mode */
> -			trynode_flags = gfpflags | __GFP_THISNODE;
> -		else
> -			trynode_flags = GFP_NOWAIT | __GFP_THISNODE;
> +		trynode_flags &= GFP_NOWAIT | __GFP_NOMEMALLOC | __GFP_ACCOUNT;
> +		trynode_flags |= __GFP_NOWARN | __GFP_THISNODE;
>  	}

-- 
Cheers,
Harry / Hyeonggon

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