linux-kernel - Re: [RFC PATCH 0/7] mm: Get rid of vmalloc_sync

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Message-ID: <20200512111332.24f5cd7a@gandalf.local.home>
Date:   Tue, 12 May 2020 11:13:32 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Joerg Roedel <jroedel@...e.de>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Joerg Roedel <joro@...tes.org>, X86 ML <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [RFC PATCH 0/7] mm: Get rid of vmalloc_sync_(un)mappings()

On Tue, 12 May 2020 17:02:50 +0200
Joerg Roedel <jroedel@...e.de> wrote:

> On Mon, May 11, 2020 at 12:36:19PM -0700, Andy Lutomirski wrote:
> > I’m guessing the right solution is either your series or your series
> > plus preallocation on 64-bit. I’m just grumpy about it...  
> 
> Okay, so we can do the pre-allocation when it turns out the pgd_list
> lock-times become a problem on x86-64. The tracking code in vmalloc.c is
> needed anyway for 32-bit and there is no reason why 64-bit shouldn't use
> it as well for now.
> I don't think that taking the lock _will_ be a problem, as it is only
> taken when a new PGD/P4D entry is populated. And it is pretty unlikely
> that a system will populate all 64 of them, with 4-level paging each of
> these entries will map 512GB of address space. But if I am wrong here
> pre-allocating is still an option.
> 

256TB of RAM isn't too far in the future ;-)

-- Steve