linux-kernel - Re: [RFC v11 09/14] mm: page_frag: use __alloc_pages() to replace alloc_pages

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Message-ID: <e7a9b79b-f1ab-4690-a3cf-4e9238e31790@huawei.com>
Date: Wed, 24 Jul 2024 20:54:57 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Alexander H Duyck <alexander.duyck@...il.com>, <davem@...emloft.net>,
	<kuba@...nel.org>, <pabeni@...hat.com>
CC: <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Andrew Morton
	<akpm@...ux-foundation.org>, <linux-mm@...ck.org>
Subject: Re: [RFC v11 09/14] mm: page_frag: use __alloc_pages() to replace
 alloc_pages_node()

On 2024/7/22 5:41, Alexander H Duyck wrote:

...

>>  	if (unlikely(!page)) {
>> -		page = alloc_pages_node(NUMA_NO_NODE, gfp, 0);
>> +		page = __alloc_pages(gfp, 0, numa_mem_id(), NULL);
>>  		if (unlikely(!page)) {
>>  			memset(nc, 0, sizeof(*nc));
>>  			return NULL;
> 
> So if I am understanding correctly this is basically just stripping the
> checks that were being performed since they aren't really needed to
> verify the output of numa_mem_id.
> 
> Rather than changing the code here, it might make more sense to update
> alloc_pages_node_noprof to move the lines from
> __alloc_pages_node_noprof into it. Then you could put the VM_BUG_ON and
> warn_if_node_offline into an else statement which would cause them to
> be automatically stripped for this and all other callers. The benefit

I suppose you meant something like below:

@@ -290,10 +290,14 @@ struct folio *__folio_alloc_node_noprof(gfp_t gfp, unsigned int order, int nid)
 static inline struct page *alloc_pages_node_noprof(int nid, gfp_t gfp_mask,
                                                   unsigned int order)
 {
-       if (nid == NUMA_NO_NODE)
+       if (nid == NUMA_NO_NODE) {
                nid = numa_mem_id();
+       } else {
+               VM_BUG_ON(nid < 0 || nid >= MAX_NUMNODES);
+               warn_if_node_offline(nid, gfp_mask);
+       }

-       return __alloc_pages_node_noprof(nid, gfp_mask, order);
+       return __alloc_pages_noprof(gfp_mask, order, nid, NULL);
 }


> would likely be much more significant and may be worthy of being
> accepted on its own merit without being a part of this patch set as I
> would imagine it would show slight gains in terms of performance and
> binary size by dropping the unnecessary instructions.

Below is the result, it does reduce the binary size for
__page_frag_alloc_align() significantly as expected, but also
increase the size for other functions, which seems to be passing
a runtime nid, so the trick above doesn't work. I am not sure if
the overall reduction is significant enough to justify the change?
It seems that depends on how many future callers are passing runtime
nid to alloc_pages_node() related APIs.

[linyunsheng@...alhost net-next]$ ./scripts/bloat-o-meter vmlinux.org vmlinux
add/remove: 1/2 grow/shrink: 13/8 up/down: 160/-256 (-96)
Function                                     old     new   delta
bpf_map_alloc_pages                          708     764     +56
its_probe_one                               2836    2860     +24
iommu_dma_alloc                              984    1008     +24
__iommu_dma_alloc_noncontiguous.constprop    1180    1192     +12
e843419@...f_00011fb1_4348                     -       8      +8
its_vpe_irq_domain_deactivate                312     316      +4
its_vpe_irq_domain_alloc                    1492    1496      +4
its_irq_domain_free                          440     444      +4
iommu_dma_map_sg                            1328    1332      +4
dpaa_eth_probe                              5524    5528      +4
dpaa2_eth_xdp_xmit                           676     680      +4
dpaa2_eth_open                               564     568      +4
dma_direct_get_required_mask                 116     120      +4
__dma_direct_alloc_pages.constprop           656     660      +4
its_vpe_set_affinity                         928     924      -4
its_send_single_command                      340     336      -4
its_alloc_table_entry                        456     452      -4
dpaa_bp_seed                                 232     228      -4
arm_64_lpae_alloc_pgtable_s1                 680     676      -4
__arm_lpae_alloc_pages                       900     896      -4
e843419@...3_00005079_16ec                     8       -      -8
e843419@...9_00001c33_1c8                      8       -      -8
ringbuf_map_alloc                            612     600     -12
__page_frag_alloc_align                      740     536    -204
Total: Before=30306836, After=30306740, chg -0.00%