From: Davidlohr Bueso <davidlohr@hp.com> To: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>, Tim Chen <tim.c.chen@linux.intel.com>, Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org>, Andrea Arcangeli <aarcange@redhat.com>, Alex Shi <alex.shi@linaro.org>, Andi Kleen <andi@firstfloor.org>, Michel Lespinasse <walken@google.com>, Davidlohr Bueso <davidlohr.bueso@hp.com>, Matthew R Wilcox <matthew.r.wilcox@intel.com>, Dave Hansen <dave.hansen@intel.com>, Rik van Riel <riel@redhat.com>, Peter Hurley <peter@hurleysoftware.com>, "Paul E.McKenney" <paulmck@linux.vnet.ibm.com>, Jason Low <jason.low2@hp.com>, Waiman Long <Waiman.Long@hp.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org> Subject: Re: [PATCH v8 0/9] rwsem performance optimizations Date: Wed, 09 Oct 2013 22:03:57 -0700 [thread overview] Message-ID: <1381381437.2297.32.camel@buesod1.americas.hpqcorp.net> (raw) In-Reply-To: <CA+55aFwECx-zQpzDunhNCd2PEbkQ7KYOfuPyzKM1X-SJ-88ZXA@mail.gmail.com> On Wed, 2013-10-09 at 20:14 -0700, Linus Torvalds wrote: > On Wed, Oct 9, 2013 at 12:28 AM, Peter Zijlstra <peterz@infradead.org> wrote: > > > > The workload that I got the report from was a virus scanner, it would > > spawn nr_cpus threads and {mmap file, scan content, munmap} through your > > filesystem. > > So I suspect we could make the mmap_sem write area *much* smaller for > the normal cases. > > Look at do_mmap_pgoff(), for example: it is run entirely under > mmap_sem, but 99% of what it does doesn't actually need the lock. > > The part that really needs the lock is > > addr = get_unmapped_area(file, addr, len, pgoff, flags); > addr = mmap_region(file, addr, len, vm_flags, pgoff); > > but we hold it over all the other stuff too. > True. By looking at the callers, we're always doing: down_write(&mm->mmap_sem); do_mmap_pgoff() ... up_write(&mm->mmap_sem); That goes for shm, aio, and of course mmap_pgoff(). While I know you hate two level locking, one way to go about this is to take the lock inside do_mmap_pgoff() after the initial checks (flags, page align, etc.) and return with the lock held, leaving the caller to unlock it. > In fact, even if we moved the mmap_sem down into do_mmap(), and moved > code around a bit to only hold it over those functions, it would still > cover unnecessarily much. For example, while merging is common, not > merging is pretty common too, and we do that > > vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL); > > allocation under the lock. We could easily do things like preallocate > it outside the lock. > AFAICT there are also checks that should be done at the beginning of the function, such as checking for MAP_LOCKED and VM_LOCKED flags before calling get_unmapped_area(). Thanks, Davidlohr
WARNING: multiple messages have this Message-ID (diff)
From: Davidlohr Bueso <davidlohr@hp.com> To: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>, Tim Chen <tim.c.chen@linux.intel.com>, Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org>, Andrea Arcangeli <aarcange@redhat.com>, Alex Shi <alex.shi@linaro.org>, Andi Kleen <andi@firstfloor.org>, Michel Lespinasse <walken@google.com>, Davidlohr Bueso <davidlohr.bueso@hp.com>, Matthew R Wilcox <matthew.r.wilcox@intel.com>, Dave Hansen <dave.hansen@intel.com>, Rik van Riel <riel@redhat.com>, Peter Hurley <peter@hurleysoftware.com>, "Paul E.McKenney" <paulmck@linux.vnet.ibm.com>, Jason Low <jason.low2@hp.com>, Waiman Long <Waiman.Long@hp.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org> Subject: Re: [PATCH v8 0/9] rwsem performance optimizations Date: Wed, 09 Oct 2013 22:03:57 -0700 [thread overview] Message-ID: <1381381437.2297.32.camel@buesod1.americas.hpqcorp.net> (raw) In-Reply-To: <CA+55aFwECx-zQpzDunhNCd2PEbkQ7KYOfuPyzKM1X-SJ-88ZXA@mail.gmail.com> On Wed, 2013-10-09 at 20:14 -0700, Linus Torvalds wrote: > On Wed, Oct 9, 2013 at 12:28 AM, Peter Zijlstra <peterz@infradead.org> wrote: > > > > The workload that I got the report from was a virus scanner, it would > > spawn nr_cpus threads and {mmap file, scan content, munmap} through your > > filesystem. > > So I suspect we could make the mmap_sem write area *much* smaller for > the normal cases. > > Look at do_mmap_pgoff(), for example: it is run entirely under > mmap_sem, but 99% of what it does doesn't actually need the lock. > > The part that really needs the lock is > > addr = get_unmapped_area(file, addr, len, pgoff, flags); > addr = mmap_region(file, addr, len, vm_flags, pgoff); > > but we hold it over all the other stuff too. > True. By looking at the callers, we're always doing: down_write(&mm->mmap_sem); do_mmap_pgoff() ... up_write(&mm->mmap_sem); That goes for shm, aio, and of course mmap_pgoff(). While I know you hate two level locking, one way to go about this is to take the lock inside do_mmap_pgoff() after the initial checks (flags, page align, etc.) and return with the lock held, leaving the caller to unlock it. > In fact, even if we moved the mmap_sem down into do_mmap(), and moved > code around a bit to only hold it over those functions, it would still > cover unnecessarily much. For example, while merging is common, not > merging is pretty common too, and we do that > > vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL); > > allocation under the lock. We could easily do things like preallocate > it outside the lock. > AFAICT there are also checks that should be done at the beginning of the function, such as checking for MAP_LOCKED and VM_LOCKED flags before calling get_unmapped_area(). Thanks, Davidlohr -- 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>
next prev parent reply other threads:[~2013-10-10 5:04 UTC|newest] Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <cover.1380748401.git.tim.c.chen@linux.intel.com> 2013-10-02 22:38 ` [PATCH v8 0/9] rwsem performance optimizations Tim Chen 2013-10-02 22:38 ` Tim Chen 2013-10-03 7:32 ` Ingo Molnar 2013-10-03 7:32 ` Ingo Molnar 2013-10-07 22:57 ` Tim Chen 2013-10-07 22:57 ` Tim Chen 2013-10-09 6:15 ` Ingo Molnar 2013-10-09 6:15 ` Ingo Molnar 2013-10-09 7:28 ` Peter Zijlstra 2013-10-09 7:28 ` Peter Zijlstra 2013-10-10 3:14 ` Linus Torvalds 2013-10-10 3:14 ` Linus Torvalds 2013-10-10 5:03 ` Davidlohr Bueso [this message] 2013-10-10 5:03 ` Davidlohr Bueso 2013-10-09 16:34 ` Tim Chen 2013-10-09 16:34 ` Tim Chen 2013-10-10 7:54 ` Ingo Molnar 2013-10-10 7:54 ` Ingo Molnar 2013-10-16 0:09 ` Tim Chen 2013-10-16 0:09 ` Tim Chen 2013-10-16 6:55 ` Ingo Molnar 2013-10-16 6:55 ` Ingo Molnar 2013-10-16 18:28 ` Tim Chen 2013-10-16 18:28 ` Tim Chen 2013-11-04 22:36 ` Tim Chen 2013-11-04 22:36 ` Tim Chen 2013-10-16 21:55 ` Tim Chen 2013-10-16 21:55 ` Tim Chen 2013-10-18 6:52 ` Ingo Molnar 2013-10-18 6:52 ` Ingo Molnar 2013-10-02 22:38 ` [PATCH v8 1/9] rwsem: check the lock before cpmxchg in down_write_trylock Tim Chen 2013-10-02 22:38 ` Tim Chen 2013-10-02 22:38 ` [PATCH v8 2/9] rwsem: remove 'out' label in do_wake Tim Chen 2013-10-02 22:38 ` Tim Chen 2013-10-02 22:38 ` [PATCH v8 3/9] rwsem: remove try_reader_grant label do_wake Tim Chen 2013-10-02 22:38 ` Tim Chen 2013-10-02 22:38 ` [PATCH v8 4/9] rwsem/wake: check lock before do atomic update Tim Chen 2013-10-02 22:38 ` Tim Chen 2013-10-02 22:38 ` [PATCH v8 5/9] MCS Lock: Restructure the MCS lock defines and locking code into its own file Tim Chen 2013-10-02 22:38 ` Tim Chen 2013-10-08 19:51 ` Rafael Aquini 2013-10-08 19:51 ` Rafael Aquini 2013-10-08 20:34 ` Tim Chen 2013-10-08 20:34 ` Tim Chen 2013-10-08 21:31 ` Rafael Aquini 2013-10-08 21:31 ` Rafael Aquini 2013-10-02 22:38 ` [PATCH v8 6/9] MCS Lock: optimizations and extra comments Tim Chen 2013-10-02 22:38 ` Tim Chen 2013-10-02 22:38 ` [PATCH v8 7/9] MCS Lock: Barrier corrections Tim Chen 2013-10-02 22:38 ` Tim Chen 2013-10-02 22:38 ` [PATCH v8 8/9] rwsem: do optimistic spinning for writer lock acquisition Tim Chen 2013-10-02 22:38 ` Tim Chen 2013-10-02 22:38 ` [PATCH v8 9/9] rwsem: reduce spinlock contention in wakeup code path Tim Chen 2013-10-02 22:38 ` Tim Chen
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