linux-kernel - Re: [PATCH v3 4/4] arm64: support batched/deferred tlb shootdown during page reclamation

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Date:   Wed, 21 Sep 2022 12:23:40 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Yicong Yang <yangyicong@...wei.com>, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
        x86@...nel.org, catalin.marinas@....com, will@...nel.org,
        linux-doc@...r.kernel.org
Cc:     corbet@....net, peterz@...radead.org, arnd@...db.de,
        linux-kernel@...r.kernel.org, darren@...amperecomputing.com,
        yangyicong@...ilicon.com, huzhanyuan@...o.com, lipeifeng@...o.com,
        zhangshiming@...o.com, guojian@...o.com, realmz6@...il.com,
        linux-mips@...r.kernel.org, openrisc@...ts.librecores.org,
        linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org, Barry Song <21cnbao@...il.com>,
        wangkefeng.wang@...wei.com, xhao@...ux.alibaba.com,
        prime.zeng@...ilicon.com, Barry Song <v-songbaohua@...o.com>,
        Nadav Amit <namit@...are.com>, Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH v3 4/4] arm64: support batched/deferred tlb shootdown
 during page reclamation


On 8/22/22 13:51, Yicong Yang wrote:
> +static inline void arch_tlbbatch_add_mm(struct arch_tlbflush_unmap_batch *batch,
> +					struct mm_struct *mm,
> +					unsigned long uaddr)
> +{
> +	__flush_tlb_page_nosync(mm, uaddr);
> +}
> +
> +static inline void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch)
> +{
> +	dsb(ish);
> +}

Just wondering if arch_tlbbatch_add_mm() could also detect continuous mapping
TLB invalidation requests on a given mm and try to generate a range based TLB
invalidation such as flush_tlb_range().

struct arch_tlbflush_unmap_batch via task->tlb_ubc->arch can track continuous
ranges while being queued up via arch_tlbbatch_add_mm(), any range formed can
later be flushed in subsequent arch_tlbbatch_flush() ?

OR

It might not be worth the effort and complexity, in comparison to performance
improvement, TLB range flush brings in ?