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Message-ID: <31546afa1e9b715f01e43a1ef9389415a8f8b05c.camel@gmail.com>
Date: Wed, 14 Aug 2024 11:34:42 -0700
From: Alexander H Duyck <alexander.duyck@...il.com>
To: Yunsheng Lin <linyunsheng@...wei.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 Thu, 2024-07-25 at 20:19 +0800, Yunsheng Lin wrote:
> 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%
One interesting similarity between the alloc_slab function and
__page_frag_alloc_align is that they both seem to be doing the higher
order followed by lower order allocation.
I wonder if we couldn't somehow consolidate the checks and make it so
that we have a function that will provide a page size within a range.
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