linux-kernel - Re: [PATCH] percpu: Sync vmalloc mappings in pcpu_alloc() and free

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Message-ID: <1533922227.82188.1588606723786.JavaMail.zimbra@efficios.com>
Date:   Mon, 4 May 2020 11:38:43 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Joerg Roedel <jroedel@...e.de>
Cc:     rostedt <rostedt@...dmis.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shile Zhang <shile.zhang@...ux.alibaba.com>,
        Andy Lutomirski <luto@...capital.net>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Tzvetomir Stoyanov <tz.stoyanov@...il.com>
Subject: Re: [PATCH] percpu: Sync vmalloc mappings in pcpu_alloc() and
 free_percpu()

----- On May 4, 2020, at 11:31 AM, Joerg Roedel jroedel@...e.de wrote:

> On Mon, May 04, 2020 at 11:28:46AM -0400, Mathieu Desnoyers wrote:
>> ----- On May 4, 2020, at 11:12 AM, Joerg Roedel jroedel@...e.de wrote:
>> Placing this here is inefficient. It syncs mappings for each percpu allocation.
>> I would recommend moving it right after __vmalloc() is called to allocate the
>> underlying memory chunk instead:
>> 
>> static void *pcpu_mem_zalloc(size_t size, gfp_t gfp)
>> {
> 
> Tried this before, actually I put it into the caller of
> pcpu_mem_zalloc(), but that didn't fix the problem for me. Stevens
> test-case still hangs the machine.

That's unexpected.

Did you confirm that those hangs were also caused by percpu allocations ?

Maybe adding the vmalloc_sync_mappings() at each percpu allocation happens
to luckily sync mappings after some other vmalloc.

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com