linux-kernel - Re: [PATCH] mremap: Increase LATENCY_LIMIT of mremap to reduce the number of TLB shootdowns

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20180606174723.bag3o55fvqp6nbvc@techsingularity.net>
Date:   Wed, 6 Jun 2018 18:47:23 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Nadav Amit <nadav.amit@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...el.com>, mhocko@...nel.org,
        vbabka@...e.cz, Aaron Lu <aaron.lu@...el.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mremap: Increase LATENCY_LIMIT of mremap to reduce the
 number of TLB shootdowns

On Wed, Jun 06, 2018 at 08:55:15AM -0700, Nadav Amit wrote:
> > -#define LATENCY_LIMIT	(64 * PAGE_SIZE)
> > +#define LATENCY_LIMIT	(PMD_SIZE)
> > 
> > unsigned long move_page_tables(struct vm_area_struct *vma,
> > 		unsigned long old_addr, struct vm_area_struct *new_vma,
> 
> This LATENCY_LIMIT is only used in move_page_tables() in the following
> manner:
> 
>   next = (new_addr + PMD_SIZE) & PMD_MASK;
>   if (extent > next - new_addr)
>       extent = next - new_addr;
>   if (extent > LATENCY_LIMIT)
>       extent = LATENCY_LIMIT;
>    
> If LATENCY_LIMIT is to be changed to PMD_SIZE, then IIUC the last condition
> is not required, and LATENCY_LIMIT can just be removed (assuming there is no
> underflow case that hides somewhere).
> 

I see no problem removing it other than we may forget that we ever limited
PTE lock hold times for any reason. I'm skeptical it will matter unless
mremap-intensive workloads are a lot more common than I believe.

-- 
Mel Gorman
SUSE Labs