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Date: Sun, 6 Jan 2019 14:12:02 +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 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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