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Date: Mon, 21 Jan 2019 13:36:00 +0530 From: Ashish Mhetre <amhetre@...dia.com> To: Matthew Wilcox <willy@...radead.org> CC: <vdumpa@...dia.com>, <mcgrof@...nel.org>, <keescook@...omium.org>, <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>, <linux-tegra@...r.kernel.org>, <Snikam@...dia.com>, <avanbrunt@...dia.com> Subject: Re: [PATCH] mm: Expose lazy vfree pages to control via sysctl The issue is not seen on new kernel. This patch won't be needed. Thanks. On 06/01/19 2:12 PM, Ashish Mhetre wrote: > Matthew, this issue was last reported in September 2018 on K4.9. > I verified that the optimization patches mentioned by you were not > present in our downstream kernel when we faced the issue. I will check > whether issue still persist on new kernel with all these patches and > come back. > > On 04/01/19 11:33 PM, Matthew Wilcox wrote: >> On Fri, Jan 04, 2019 at 09:05:41PM +0530, Ashish Mhetre wrote: >>> From: Hiroshi Doyu <hdoyu@...dia.com> >>> >>> The purpose of lazy_max_pages is to gather virtual address space till it >>> reaches the lazy_max_pages limit and then purge with a TLB flush and >>> hence >>> reduce the number of global TLB flushes. >>> The default value of lazy_max_pages with one CPU is 32MB and with 4 >>> CPUs it >>> is 96MB i.e. for 4 cores, 96MB of vmalloc space will be gathered >>> before it >>> is purged with a TLB flush. >>> This feature has shown random latency issues. For example, we have seen >>> that the kernel thread for some camera application spent 30ms in >>> __purge_vmap_area_lazy() with 4 CPUs. >> >> You're not the first to report something like this. Looking through the >> kernel logs, I see: >> >> commit 763b218ddfaf56761c19923beb7e16656f66ec62 >> Author: Joel Fernandes <joelaf@...gle.com> >> Date: Mon Dec 12 16:44:26 2016 -0800 >> >> mm: add preempt points into __purge_vmap_area_lazy() >> >> commit f9e09977671b618aeb25ddc0d4c9a84d5b5cde9d >> Author: Christoph Hellwig <hch@....de> >> Date: Mon Dec 12 16:44:23 2016 -0800 >> >> mm: turn vmap_purge_lock into a mutex >> >> commit 80c4bd7a5e4368b680e0aeb57050a1b06eb573d8 >> Author: Chris Wilson <chris@...is-wilson.co.uk> >> Date: Fri May 20 16:57:38 2016 -0700 >> >> mm/vmalloc: keep a separate lazy-free list >> >> So the first thing I want to do is to confirm that you see this problem >> on a modern kernel. We've had trouble with NVidia before reporting >> historical problems as if they were new. >>
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