Re: [PATCH 1/1] mm/page_alloc: auto-tune min_free_kbytes on atomic allocation failure

[Lance Yang <lance.yang@linux.dev>]

On Sun,  4 Jan 2026 20:26:52 +0800, wujing wrote:
> Introduce a mechanism to dynamically increase vm.min_free_kbytes when
> critical atomic allocations (GFP_ATOMIC, order-0) fail. This prevents
> recurring network packet drops or other atomic failures by proactively
> reserving more memory.

Just wondering, could we adjust watermark_scale_factor instead of
min_free_kbytes?

Increasing min_free_kbytes directly reduces available memory, while
watermark_scale_factor just makes kswapd wake up earlier for reclaim ...

Seems like less side effect than min_free_kbytes :)

Cheers,
Lance

> 
> The adjustment doubles min_free_kbytes upon upon failure (exponential backoff),
> capped at 1% of total RAM.
> 
> Observed failure logs:
> [38535641.026406] node 0: slabs: 941, objs: 54656, free: 0
> [38535641.037711] node 1: slabs: 349, objs: 22096, free: 272
> [38535641.049025] node 1: slabs: 349, objs: 22096, free: 272
> [38535642.795972] SLUB: Unable to allocate memory on node -1, gfp=0x480020(GFP_ATOMIC)
> [38535642.805017] cache: skbuff_head_cache, object size: 232, buffer size: 256, default order: 2, min order: 0
> [38535642.816311] node 0: slabs: 854, objs: 42320, free: 0
> [38535642.823066] node 1: slabs: 400, objs: 25360, free: 294
> [38535643.070199] SLUB: Unable to allocate memory on node -1, gfp=0x480020(GFP_ATOMIC)
> [38535643.078861] cache: skbuff_head_cache, object size: 232, buffer size: 256, default order: 2, min order: 0
> [38535643.089719] node 0: slabs: 841, objs: 41824, free: 0
> [38535643.096513] node 1: slabs: 393, objs: 24480, free: 272
> [38535643.484149] SLUB: Unable to allocate memory on node -1, gfp=0x480020(GFP_ATOMIC)
> [38535643.492831] cache: skbuff_head_cache, object size: 232, buffer size: 256, default order: 2, min order: 0
> [38535643.503666] node 0: slabs: 898, objs: 43120, free: 159
> [38535643.510140] node 1: slabs: 404, objs: 25424, free: 319
> [38535644.699224] SLUB: Unable to allocate memory on node -1, gfp=0x480020(GFP_ATOMIC)
> [38535644.707911] cache: skbuff_head_cache, object size: 232, buffer size: 256, default order: 2, min order: 0
> [38535644.718700] node 0: slabs: 1031, objs: 43328, free: 0
> [38535644.725059] node 1: slabs: 339, objs: 17616, free: 317
> [38535645.428345] SLUB: Unable to allocate memory on node -1, gfp=0x480020(GFP_ATOMIC)
> [38535645.436888] cache: skbuff_head_cache, object size: 232, buffer size: 256, default order: 2, min order: 0
> [38535645.447664] node 0: slabs: 940, objs: 40864, free: 144
> [38535645.454026] node 1: slabs: 322, objs: 19168, free: 383
> [38535645.556122] SLUB: Unable to allocate memory on node -1, gfp=0x480020(GFP_ATOMIC)
> [38535645.564576] cache: skbuff_head_cache, object size: 232, buffer size: 256, default order: 2, min order: 0
> [38535649.655523] warn_alloc: 59 callbacks suppressed
> [38535649.655527] swapper/100: page allocation failure: order:0, mode:0x480020(GFP_ATOMIC), nodemask=(null)
> [38535649.671692] swapper/100 cpuset=/ mems_allowed=0-1
> 
> Signed-off-by: wujing <realwujing@qq.com>
> Signed-off-by: Qiliang Yuan <yuanql9@chinatelecom.cn>
> ---
>  mm/page_alloc.c | 33 +++++++++++++++++++++++++++++++++
>  1 file changed, 33 insertions(+)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c380f063e8b7..9a24e2b6cfbf 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -30,6 +30,7 @@
>  #include <linux/oom.h>
>  #include <linux/topology.h>
>  #include <linux/sysctl.h>
> +#include <linux/workqueue.h>
>  #include <linux/cpu.h>
>  #include <linux/cpuset.h>
>  #include <linux/pagevec.h>
> @@ -3975,6 +3976,9 @@ static void warn_alloc_show_mem(gfp_t gfp_mask, nodemask_t *nodemask)
>  	mem_cgroup_show_protected_memory(NULL);
>  }
>  
> +static void boost_min_free_kbytes_workfn(struct work_struct *work);
> +static DECLARE_WORK(boost_min_free_kbytes_work, boost_min_free_kbytes_workfn);
> +
>  void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...)
>  {
>  	struct va_format vaf;
> @@ -4947,6 +4951,10 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>  		goto retry;
>  	}
>  fail:
> +	/* Auto-tuning: trigger boost if atomic allocation fails */
> +	if ((gfp_mask & GFP_ATOMIC) && order == 0)
> +		schedule_work(&boost_min_free_kbytes_work);
> +
>  	warn_alloc(gfp_mask, ac->nodemask,
>  			"page allocation failure: order:%u", order);
>  got_pg:
> @@ -7682,3 +7690,28 @@ struct page *alloc_pages_nolock_noprof(gfp_t gfp_flags, int nid, unsigned int or
>  	return page;
>  }
>  EXPORT_SYMBOL_GPL(alloc_pages_nolock_noprof);
> +
> +static void boost_min_free_kbytes_workfn(struct work_struct *work)
> +{
> +	int new_min;
> +
> +	/* Cap at 1% of total RAM for safety */
> +	unsigned long total_kbytes = totalram_pages() << (PAGE_SHIFT - 10);
> +	int max_limit = total_kbytes / 100;
> +
> +	/* Exponential increase: double the current value */
> +	new_min = min_free_kbytes * 2;
> +
> +	if (new_min > max_limit)
> +		new_min = max_limit;
> +
> +	if (new_min > min_free_kbytes) {
> +		min_free_kbytes = new_min;
> +		/* Update user_min_free_kbytes so it persists through recalculations */
> +		if (new_min > user_min_free_kbytes)
> +			user_min_free_kbytes = new_min;
> +		
> +		setup_per_zone_wmarks();
> +		pr_info("Auto-tuning: unexpected atomic failure detected, increasing min_free_kbytes to %d\n", min_free_kbytes);
> +	}
> +}