linux-kernel - Re: [PATCH v2 0/5] mm: support parallel free of memory

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Date:   Mon, 20 Mar 2017 14:15:36 -0500
From:   Alex Thorlton <alex.thorlton@....com>
To:     Aaron Lu <aaron.lu@...el.com>
CC:     Alex Thorlton <alex.thorlton@....com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Tim Chen <tim.c.chen@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ying Huang <ying.huang@...el.com>
Subject: Re: [PATCH v2 0/5] mm: support parallel free of memory

On Fri, Mar 17, 2017 at 10:21:58AM +0800, Aaron Lu wrote:
> On Thu, Mar 16, 2017 at 02:38:44PM -0500, Alex Thorlton wrote:
> > On Wed, Mar 15, 2017 at 04:59:59PM +0800, Aaron Lu wrote:
> > > v2 changes: Nothing major, only minor ones.
> > >  - rebased on top of v4.11-rc2-mmotm-2017-03-14-15-41;
> > >  - use list_add_tail instead of list_add to add worker to tlb's worker
> > >    list so that when doing flush, the first queued worker gets flushed
> > >    first(based on the comsumption that the first queued worker has a
> > >    better chance of finishing its job than those later queued workers);
> > >  - use bool instead of int for variable free_batch_page in function
> > >    tlb_flush_mmu_free_batches;
> > >  - style change according to ./scripts/checkpatch;
> > >  - reword some of the changelogs to make it more readable.
> > > 
> > > v1 is here:
> > > https://lkml.org/lkml/2017/2/24/245
> > 
> > I tested v1 on a Haswell system with 64 sockets/1024 cores/2048 threads
> > and 8TB of RAM, with a 1TB malloc.  The average free() time for a 1TB
> > malloc on a vanilla kernel was 41.69s, the patched kernel averaged
> > 21.56s for the same test.
> 
> Thanks a lot for the test result.
> 
> > 
> > I am testing v2 now and will report back with results in the next day or
> > so.
> 
> Testing plain v2 shouldn't bring any surprise/difference

You're right!  Not much difference here.  v2 averaged a 23.17s free
time for a 1T allocation.

> better set the
> following param before the test(I'm planning to make them default in the
> next version):
> # echo 64 > /sys/devices/virtual/workqueue/batch_free_wq/max_active
> # echo 1030 > /sys/kernel/debug/parallel_free/max_gather_batch_count

10 test runs with these params set averaged 22.22s to free 1T.

So, we're still seeing a nearly 50% decrease in free time vs. the
unpatched kernel.

- Alex