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Date:   Tue, 12 May 2020 17:02:50 +0200
From:   Joerg Roedel <jroedel@suse.de>
To:     Andy Lutomirski <luto@amacapital.net>
Cc:     Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Joerg Roedel <joro@8bytes.org>, X86 ML <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Arnd Bergmann <arnd@arndb.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Michal Hocko <mhocko@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux ACPI <linux-acpi@vger.kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>
Subject: Re: [RFC PATCH 0/7] mm: Get rid of vmalloc_sync_(un)mappings()
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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.


	Joerg