Messages in this thread | | | Date | Tue, 5 Jul 2022 21:17:48 +0800 | Subject | Re: [PATCH v4] arm64: mm: fix linear mem mapping access performance degradation | From | "guanghui.fgh" <> |
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在 2022/7/5 20:56, Mike Rapoport 写道: > On Tue, Jul 05, 2022 at 01:11:16PM +0100, Will Deacon wrote: >> On Tue, Jul 05, 2022 at 08:07:07PM +0800, guanghui.fgh wrote: >>> >>> 1.The rodata full is harm to the performance and has been disabled in-house. >>> >>> 2.When using crashkernel with rodata non full, the kernel also will use non >>> block/section mapping which cause high d-TLB miss and degrade performance >>> greatly. >>> This patch fix it to use block/section mapping as far as possible. >>> >>> bool can_set_direct_map(void) >>> { >>> return rodata_full || debug_pagealloc_enabled(); >>> } >>> >>> map_mem: >>> if (can_set_direct_map() || IS_ENABLED(CONFIG_KFENCE)) >>> flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS; >>> >>> 3.When rodata full is disabled, crashkernel also need protect(keep >>> arch_kexec_[un]protect_crashkres using). >>> I think crashkernel should't depend on radata full(Maybe other architecture >>> don't support radata full now). >> >> I think this is going round in circles :/ >> >> As a first step, can we please leave the crashkernel mapped unless >> rodata=full? It should be a much simpler patch to write, review and maintain >> and it gives you the performance you want when crashkernel is being used. > > Since we are talking about large systems, what do you think about letting > them set CRASH_ALIGN to PUD_SIZE, then > > unmap(crashkernel); > __create_pgd_mapping(crashkernel, NO_BLOCK_MAPPINGS); > > should be enough to make crash kernel mapped with base pages. > >> Will > Thanks.
1.When kernel boots with crashkernel, the crashkernel parameters format is: 0M-2G:0M,2G-256G:256M,256G-1024G:320M,1024G-:384M which is self-adaption to multiple system.
2.As mentioned above, the crashkernel mem size maybe less than PUD_SIZE(Not multiple time to PUD_SIZE). So, maybe we also need use some non block/section mappings.
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