linux-kernel - Re: [PATCH bpf-next 1/4] bpf: tailcall: Introduce bpf_arch_tail_call_prologue

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Message-ID: <883a21af-750c-49df-88c6-47bd642e03d4@linux.dev>
Date: Fri, 2 Jan 2026 23:38:25 +0800
From: Leon Hwang <leon.hwang@...ux.dev>
To: bot+bpf-ci@...nel.org, bpf@...r.kernel.org
Cc: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
 martin.lau@...ux.dev, eddyz87@...il.com, song@...nel.org,
 yonghong.song@...ux.dev, john.fastabend@...il.com, kpsingh@...nel.org,
 sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org, puranjay@...nel.org,
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 davem@...emloft.net, dsahern@...nel.org, tglx@...utronix.de,
 mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
 hpa@...or.com, akpm@...ux-foundation.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 netdev@...r.kernel.org, kernel-patches-bot@...com, martin.lau@...nel.org,
 clm@...a.com, ihor.solodrai@...ux.dev
Subject: Re: [PATCH bpf-next 1/4] bpf: tailcall: Introduce
 bpf_arch_tail_call_prologue_offset



On 2026/1/2 23:21, bot+bpf-ci@...nel.org wrote:
>> diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
>> index 1eeb31c5b317..beedd1281c22 100644
>> --- a/kernel/bpf/arraymap.c
>> +++ b/kernel/bpf/arraymap.c
>> @@ -127,6 +127,9 @@ static struct bpf_map *array_map_alloc(union bpf_attr *attr)
>>  			array_size += (u64) max_entries * elem_size;
>>  		}
>>  	}
>> +	if (attr->map_type == BPF_MAP_TYPE_PROG_ARRAY && bpf_arch_tail_call_prologue_offset())
>> +		/* Store tailcall targets */
>> +		array_size += (u64) max_entries * sizeof(void *);
> 
> Should array_map_mem_usage() also account for this additional space?
> Currently array_map_mem_usage() handles special cases for percpu arrays
> and mmapable arrays, but has no corresponding check for PROG_ARRAY maps
> when bpf_arch_tail_call_prologue_offset() is non-zero. This would cause
> the reported memory usage to be lower than the actual allocation when
> an architecture implements this function (e.g., x86_64 and arm64 in the
> subsequent patches of this series).
> 
> [ ... ]
> 

You are right, array_map_mem_usage() needs to stay in sync with the
allocation logic to avoid under-reporting memory.

I will include this fix in the next revision after I’ve collected more
feedback.

Thanks,
Leon