From: Peter Zijlstra <peterz@infradead.org> To: Nadav Amit <namit@vmware.com> Cc: "open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Andrew Morton <akpm@linux-foundation.org>, Minchan Kim <minchan@kernel.org>, Ingo Molnar <mingo@redhat.com>, Russell King <linux@armlinux.org.uk>, Tony Luck <tony.luck@intel.com>, Martin Schwidefsky <schwidefsky@de.ibm.com>, "David S. Miller" <davem@davemloft.net>, Heiko Carstens <heiko.carstens@de.ibm.com>, Yoshinori Sato <ysato@users.sourceforge.jp>, Jeff Dike <jdike@addtoit.com>, "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org> Subject: Re: [PATCH v6 6/7] mm: fix MADV_[FREE|DONTNEED] TLB flush miss problem Date: Sun, 13 Aug 2017 14:08:08 +0200 [thread overview] Message-ID: <20170813120808.ph4zlz5u4p2edqev@hirez.programming.kicks-ass.net> (raw) In-Reply-To: <E340B75B-2830-4E6D-BF0A-2C58A7002CF1@vmware.com> On Sun, Aug 13, 2017 at 06:14:21AM +0000, Nadav Amit wrote: > Peter Zijlstra <peterz@infradead.org> wrote: > > > On Tue, Aug 01, 2017 at 05:08:17PM -0700, Nadav Amit wrote: > >> void tlb_finish_mmu(struct mmu_gather *tlb, > >> unsigned long start, unsigned long end) > >> { > >> - arch_tlb_finish_mmu(tlb, start, end); > >> + /* > >> + * If there are parallel threads are doing PTE changes on same range > >> + * under non-exclusive lock(e.g., mmap_sem read-side) but defer TLB > >> + * flush by batching, a thread has stable TLB entry can fail to flush > >> + * the TLB by observing pte_none|!pte_dirty, for example so flush TLB > >> + * forcefully if we detect parallel PTE batching threads. > >> + */ > >> + bool force = mm_tlb_flush_nested(tlb->mm); > >> + > >> + arch_tlb_finish_mmu(tlb, start, end, force); > >> } > > > > I don't understand the comment nor the ordering. What guarantees we see > > the increment if we need to? > > The comment regards the problem that is described in the change-log, and a > long thread that is referenced in it. So the question is whether “I don’t > understand” means “I don’t understand” or “it is not clear enough”. I’ll > be glad to address either one - just say which. I only read the comment, that _should_ be sufficient. Comments that rely on Changelogs and random threads are useless. The comment on its own simply doesn't make sense. > As for the ordering - I tried to clarify it in the thread of the commit. Let > me know if it is clear now. Yeah, I'll do a new patch because if it only cares about _the_ PTL, we can do away with that extra smp_mb__after_atomic(). -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org> To: Nadav Amit <namit@vmware.com> Cc: "open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Andrew Morton <akpm@linux-foundation.org>, Minchan Kim <minchan@kernel.org>, Ingo Molnar <mingo@redhat.com>, Russell King <linux@armlinux.org.uk>, Tony Luck <tony.luck@intel.com>, Martin Schwidefsky <schwidefsky@de.ibm.com>, "David S. Miller" <davem@davemloft.net>, Heiko Carstens <heiko.carstens@de.ibm.com>, Yoshinori Sato <ysato@users.sourceforge.jp>, Jeff Dike <jdike@addtoit.com>, "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org> Subject: Re: [PATCH v6 6/7] mm: fix MADV_[FREE|DONTNEED] TLB flush miss problem Date: Sun, 13 Aug 2017 14:08:08 +0200 [thread overview] Message-ID: <20170813120808.ph4zlz5u4p2edqev@hirez.programming.kicks-ass.net> (raw) Message-ID: <20170813120808.4JKYRwHNIfDNGf_H6Eb5TJp_vYYWuQCVgc69XLPjRw4@z> (raw) In-Reply-To: <E340B75B-2830-4E6D-BF0A-2C58A7002CF1@vmware.com> On Sun, Aug 13, 2017 at 06:14:21AM +0000, Nadav Amit wrote: > Peter Zijlstra <peterz@infradead.org> wrote: > > > On Tue, Aug 01, 2017 at 05:08:17PM -0700, Nadav Amit wrote: > >> void tlb_finish_mmu(struct mmu_gather *tlb, > >> unsigned long start, unsigned long end) > >> { > >> - arch_tlb_finish_mmu(tlb, start, end); > >> + /* > >> + * If there are parallel threads are doing PTE changes on same range > >> + * under non-exclusive lock(e.g., mmap_sem read-side) but defer TLB > >> + * flush by batching, a thread has stable TLB entry can fail to flush > >> + * the TLB by observing pte_none|!pte_dirty, for example so flush TLB > >> + * forcefully if we detect parallel PTE batching threads. > >> + */ > >> + bool force = mm_tlb_flush_nested(tlb->mm); > >> + > >> + arch_tlb_finish_mmu(tlb, start, end, force); > >> } > > > > I don't understand the comment nor the ordering. What guarantees we see > > the increment if we need to? > > The comment regards the problem that is described in the change-log, and a > long thread that is referenced in it. So the question is whether “I don’t > understand” means “I don’t understand” or “it is not clear enough”. I’ll > be glad to address either one - just say which. I only read the comment, that _should_ be sufficient. Comments that rely on Changelogs and random threads are useless. The comment on its own simply doesn't make sense. > As for the ordering - I tried to clarify it in the thread of the commit. Let > me know if it is clear now. Yeah, I'll do a new patch because if it only cares about _the_ PTL, we can do away with that extra smp_mb__after_atomic().
next prev parent reply other threads:[~2017-08-13 12:08 UTC|newest] Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <20170802000818.4760-1-namit@vmware.com> 2017-08-02 0:08 ` [PATCH v6 4/7] mm: refactoring TLB gathering API Nadav Amit 2017-08-02 0:08 ` Nadav Amit 2017-08-11 9:23 ` Peter Zijlstra 2017-08-11 9:23 ` Peter Zijlstra 2017-08-11 17:12 ` Nadav Amit 2017-08-11 17:12 ` Nadav Amit 2017-08-14 0:49 ` Minchan Kim 2017-08-02 0:08 ` [PATCH v6 6/7] mm: fix MADV_[FREE|DONTNEED] TLB flush miss problem Nadav Amit 2017-08-02 0:08 ` Nadav Amit 2017-08-08 1:19 ` [lkp-robot] [mm] 7674270022: will-it-scale.per_process_ops -19.3% regression kernel test robot 2017-08-08 2:28 ` Minchan Kim 2017-08-08 2:28 ` Minchan Kim 2017-08-08 4:23 ` Nadav Amit 2017-08-08 4:23 ` Nadav Amit 2017-08-08 5:51 ` Nadav Amit 2017-08-08 5:51 ` Nadav Amit 2017-08-08 8:08 ` Minchan Kim 2017-08-08 8:08 ` Minchan Kim 2017-08-08 8:16 ` Nadav Amit 2017-08-09 1:25 ` Ye Xiaolong 2017-08-09 2:59 ` Ye Xiaolong 2017-08-09 2:59 ` Ye Xiaolong 2017-08-10 4:13 ` Minchan Kim 2017-08-10 4:13 ` Minchan Kim 2017-08-10 4:14 ` Nadav Amit 2017-08-10 4:14 ` Nadav Amit 2017-08-10 4:20 ` Minchan Kim 2017-08-11 13:30 ` [PATCH v6 6/7] mm: fix MADV_[FREE|DONTNEED] TLB flush miss problem Peter Zijlstra 2017-08-11 13:30 ` Peter Zijlstra 2017-08-13 6:14 ` Nadav Amit 2017-08-13 6:14 ` Nadav Amit 2017-08-13 12:08 ` Peter Zijlstra [this message] 2017-08-13 12:08 ` Peter Zijlstra 2017-08-14 1:26 ` Minchan Kim 2017-08-14 1:26 ` Minchan Kim
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