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

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Message-ID: <20200509175448.GW8135@suse.de>
Date:   Sat, 9 May 2020 19:54:48 +0200
From:   Joerg Roedel <jroedel@...e.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Joerg Roedel <joro@...tes.org>, x86@...nel.org, hpa@...or.com,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>, rjw@...ysocki.net,
        Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...nel.org>, linux-kernel@...r.kernel.org,
        linux-acpi@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [RFC PATCH 0/7] mm: Get rid of vmalloc_sync_(un)mappings()

On Sat, May 09, 2020 at 11:25:16AM +0200, Peter Zijlstra wrote:
> Right; it's just that the moment you do trigger it, it'll iterate that
> pgd_list and that is potentially huge. Then again, that's not a new
> problem.
> 
> I suppose we can deal with it if/when it becomes an actual problem.
> 
> I had a quick look and I think it might be possible to make it an RCU
> managed list. We'd have to remove the pgd_list entry in
> put_task_struct_rcu_user(). Then we can play games in sync_global_*()
> and use RCU iteration. New tasks (which can be missed in the RCU
> iteration) will already have a full clone of the PGD anyway.

Right, it should not be that difficult to rcu-protect the pgd-list, but
we can try that when it actually becomes a problem.


	Joerg