Re: [PATCH 28/28] mm, page_alloc: Defer debugging checks of pages allocated from the PCP

[Vlastimil Babka]

On 04/15/2016 11:07 AM, Mel Gorman wrote:
> Every page allocated checks a number of page fields for validity. This
> catches corruption bugs of pages that are already freed but it is expensive.
> This patch weakens the debugging check by checking PCP pages only when
> the PCP lists are being refilled. All compound pages are checked. This
> potentially avoids debugging checks entirely if the PCP lists are never
> emptied and refilled so some corruption issues may be missed. Full checking
> requires DEBUG_VM.
> 
> With the two deferred debugging patches applied, the impact to a page
> allocator microbenchmark is
> 
>                                             4.6.0-rc3                  4.6.0-rc3
>                                           inline-v3r6            deferalloc-v3r7
> Min      alloc-odr0-1               344.00 (  0.00%)           317.00 (  7.85%)
> Min      alloc-odr0-2               248.00 (  0.00%)           231.00 (  6.85%)
> Min      alloc-odr0-4               209.00 (  0.00%)           192.00 (  8.13%)
> Min      alloc-odr0-8               181.00 (  0.00%)           166.00 (  8.29%)
> Min      alloc-odr0-16              168.00 (  0.00%)           154.00 (  8.33%)
> Min      alloc-odr0-32              161.00 (  0.00%)           148.00 (  8.07%)
> Min      alloc-odr0-64              158.00 (  0.00%)           145.00 (  8.23%)
> Min      alloc-odr0-128             156.00 (  0.00%)           143.00 (  8.33%)
> Min      alloc-odr0-256             168.00 (  0.00%)           154.00 (  8.33%)
> Min      alloc-odr0-512             178.00 (  0.00%)           167.00 (  6.18%)
> Min      alloc-odr0-1024            186.00 (  0.00%)           174.00 (  6.45%)
> Min      alloc-odr0-2048            192.00 (  0.00%)           180.00 (  6.25%)
> Min      alloc-odr0-4096            198.00 (  0.00%)           184.00 (  7.07%)
> Min      alloc-odr0-8192            200.00 (  0.00%)           188.00 (  6.00%)
> Min      alloc-odr0-16384           201.00 (  0.00%)           188.00 (  6.47%)
> Min      free-odr0-1                189.00 (  0.00%)           180.00 (  4.76%)
> Min      free-odr0-2                132.00 (  0.00%)           126.00 (  4.55%)
> Min      free-odr0-4                104.00 (  0.00%)            99.00 (  4.81%)
> Min      free-odr0-8                 90.00 (  0.00%)            85.00 (  5.56%)
> Min      free-odr0-16                84.00 (  0.00%)            80.00 (  4.76%)
> Min      free-odr0-32                80.00 (  0.00%)            76.00 (  5.00%)
> Min      free-odr0-64                78.00 (  0.00%)            74.00 (  5.13%)
> Min      free-odr0-128               77.00 (  0.00%)            73.00 (  5.19%)
> Min      free-odr0-256               94.00 (  0.00%)            91.00 (  3.19%)
> Min      free-odr0-512              108.00 (  0.00%)           112.00 ( -3.70%)
> Min      free-odr0-1024             115.00 (  0.00%)           118.00 ( -2.61%)
> Min      free-odr0-2048             120.00 (  0.00%)           125.00 ( -4.17%)
> Min      free-odr0-4096             123.00 (  0.00%)           129.00 ( -4.88%)
> Min      free-odr0-8192             126.00 (  0.00%)           130.00 ( -3.17%)
> Min      free-odr0-16384            126.00 (  0.00%)           131.00 ( -3.97%)
> 
> Note that the free paths for large numbers of pages is impacted as the
> debugging cost gets shifted into that path when the page data is no longer
> necessarily cache-hot.
> 
> Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

Unlike the free path, there are no duplications here, which is nice.
Some un-inlining of bad page check should still work here though imho: