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 QCDfAQVS 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: David Hildenbrand (Red Hat) writes: > On 10.11.25 08:20, Ankur Arora wrote: >> David Hildenbrand (Red Hat) writes: >> >>> On 27.10.25 21:21, Ankur Arora wrote: >>>> Clear contiguous page ranges in folio_zero_user() instead of clearing >>>> a page-at-a-time. This enables CPU specific optimizations based on >>>> the length of the region. >>>> Operating on arbitrarily large regions can lead to high preemption >>>> latency under cooperative preemption models. So, limit the worst >>>> case preemption latency via architecture specified PAGE_CONTIG_NR >>>> units. >>>> The resultant performance depends on the kinds of optimizations >>>> available to the CPU for the region being cleared. Two classes of >>>> of optimizations: >>>> - clearing iteration costs can be amortized over a range larger >>>> than a single page. >>>> - cacheline allocation elision (seen on AMD Zen models). >>>> Testing a demand fault workload shows an improved baseline from the >>>> first optimization and a larger improvement when the region being >>>> cleared is large enough for the second optimization. >>>> AMD Milan (EPYC 7J13, boost=0, region=64GB on the local NUMA node): >>>> $ perf bench mem map -p $pg-sz -f demand -s 64GB -l 5 >>>> page-at-a-time contiguous clearing change >>>> (GB/s +- %stdev) (GB/s +- %stdev) >>>> pg-sz=2MB 12.92 +- 2.55% 17.03 +- 0.70% + 31.8% >>>> preempt=* >>>> pg-sz=1GB 17.14 +- 2.27% 18.04 +- 1.05% [#] + 5.2% >>>> preempt=none|voluntary >>>> pg-sz=1GB 17.26 +- 1.24% 42.17 +- 4.21% +144.3% preempt=full|lazy >>>> [#] AMD Milan uses a threshold of LLC-size (~32MB) for eliding cacheline >>>> allocation, which is larger than ARCH_PAGE_CONTIG_NR, so >>>> preempt=none|voluntary see no improvement on the pg-sz=1GB. >>>> Also as mentioned earlier, the baseline improvement is not specific to >>>> AMD Zen platforms. Intel Icelakex (pg-sz=2MB|1GB) sees a similar >>>> improvement as the Milan pg-sz=2MB workload above (~30%). >>>> Signed-off-by: Ankur Arora >>>> Reviewed-by: Raghavendra K T >>>> Tested-by: Raghavendra K T >>>> --- >>>> include/linux/mm.h | 6 ++++++ >>>> mm/memory.c | 42 +++++++++++++++++++++--------------------- >>>> 2 files changed, 27 insertions(+), 21 deletions(-) >>>> diff --git a/include/linux/mm.h b/include/linux/mm.h >>>> index ecbcb76df9de..02db84667f97 100644 >>>> --- a/include/linux/mm.h >>>> +++ b/include/linux/mm.h >>>> @@ -3872,6 +3872,12 @@ static inline void clear_page_guard(struct zone *zone, struct page *page, >>>> unsigned int order) {} >>>> #endif /* CONFIG_DEBUG_PAGEALLOC */ >>>> +#ifndef ARCH_PAGE_CONTIG_NR >>>> +#define PAGE_CONTIG_NR 1 >>>> +#else >>>> +#define PAGE_CONTIG_NR ARCH_PAGE_CONTIG_NR >>>> +#endif >>> >>> The name is a bit misleading. We need something that tells us that this is for >>> patch-processing (clearing? maybe alter copying?) contig pages. Likely spelling >>> out that this is for the non-preemptible case only. >>> >>> I assume we can drop the "CONTIG", just like clear_pages() doesn't contain it >>> etc. >>> >>> CLEAR_PAGES_NON_PREEMPT_BATCH >>> >>> PROCESS_PAGES_NON_PREEMPT_BATCH >> I think this version is clearer. And would be viable for copying as well. >> >>> Can you remind me again why this is arch specific, and why the default is 1 >>> instead of, say 2,4,8 ... ? >> So, the only use for this value is to decide a reasonable frequency >> for calling cond_resched() when operating on hugepages. >> And the idea was the arch was best placed to have a reasonably safe >> value based on the expected spread of bandwidths it might see across >> uarchs. And the default choice of 1 was to keep it close to what we >> have now. >> Thinking about it now though, maybe it is better to instead do this >> in common code. We could have two sets of defines, >> PROCESS_PAGES_NON_PREEMPT_BATCH_{LARGE,SMALL}, the first for archs >> that define __HAVE_ARCH_CLEAR_PAGES and the second, without. > > Right, avoiding this dependency on arch code would be nice. > > Also, it feels like something we can later optimize for archs without > __HAVE_ARCH_CLEAR_PAGES in common code. That makes sense. Will keep the default where it is (1) and just get rid of the arch dependency. -- ankur