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Message-ID: <5df99f22-801c-4b0a-a3bc-0e2e0fadfdd3@huawei.com>
Date: Thu, 25 Jul 2024 20:19:12 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Alexander Duyck <alexander.duyck@...il.com>
CC: <davem@...emloft.net>, <kuba@...nel.org>, <pabeni@...hat.com>,
<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 2024/7/24 23:03, Alexander Duyck wrote:
> On Wed, Jul 24, 2024 at 5:55 AM Yunsheng Lin <linyunsheng@...wei.com> wrote:
>>
>> 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);
>> }
>
> Yes, that is more or less what I was thinking.
>
>>> 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%
>
> I'm assuming the compiler must have uninlined
> __alloc_pages_node_noprof in the previous version of things for the
> cases where it is causing an increase in the code size.
>
> One alternative approach we could look at doing would be to just add
> the following to the start of the function:
> if (__builtin_constant_p(nid) && nid == NUMA_NO_NODE)
> return __alloc_pages_noprof(gfp_mask, order, numa_mem_id(), NULL);
>
> That should yield the best result as it essentially skips over the
> problematic code at compile time for the constant case, otherwise the
> code should be fully stripped so it shouldn't add any additional
> overhead.
Just tried it, it seems it is more complicated than expected too.
For example, the above changing seems to cause alloc_slab_page() to be
inlined to new_slab() and other inlining/uninlining that is hard to
understand.
[linyunsheng@...alhost net-next]$ ./scripts/bloat-o-meter vmlinux.org vmlinux
add/remove: 1/2 grow/shrink: 16/11 up/down: 432/-536 (-104)
Function old new delta
new_slab 808 1124 +316
its_probe_one 2836 2876 +40
dpaa2_eth_set_dist_key 1096 1112 +16
e843419@...f_00011fb1_4348 - 8 +8
rx_default_dqrr 2776 2780 +4
pcpu_unmap_pages 356 360 +4
its_vpe_irq_domain_alloc 1492 1496 +4
iommu_dma_init_fq 520 524 +4
iommu_dma_alloc 984 988 +4
hns3_nic_net_timeout 704 708 +4
hns3_init_all_ring 1168 1172 +4
hns3_clear_all_ring 372 376 +4
enetc_refill_rx_ring 448 452 +4
enetc_free_rxtx_rings 276 280 +4
dpaa2_eth_xdp_xmit 676 680 +4
dpaa2_eth_rx 1716 1720 +4
___slab_alloc 2120 2124 +4
pcpu_free_pages.constprop 236 232 -4
its_alloc_table_entry 456 452 -4
hns3_reset_notify_init_enet 628 624 -4
dpaa_cleanup_tx_fd 556 552 -4
dpaa_bp_seed 232 228 -4
blk_update_request 944 940 -4
blk_execute_rq 540 536 -4
arm_64_lpae_alloc_pgtable_s1 680 676 -4
__kmalloc_large_node 340 336 -4
__arm_lpae_unmap 1588 1584 -4
e843419@...3_00005079_16ec 8 - -8
__page_frag_alloc_align 740 536 -204
alloc_slab_page 284 - -284
Total: Before=30306836, After=30306732, chg -0.00%
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