linux-kernel - Re: [PATCH] Increase default MLOCK

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Message-ID: <20211124132842.GH5112@ziepe.ca>
Date:   Wed, 24 Nov 2021 09:28:42 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     David Hildenbrand <david@...hat.com>
Cc:     Vlastimil Babka <vbabka@...e.cz>, Jens Axboe <axboe@...nel.dk>,
        Andrew Dona-Couch <andrew@...acou.ch>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Drew DeVault <sir@...wn.com>,
        Ammar Faizi <ammarfaizi2@...weeb.org>,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        io_uring Mailing List <io-uring@...r.kernel.org>,
        Pavel Begunkov <asml.silence@...il.com>, linux-mm@...ck.org
Subject: Re: [PATCH] Increase default MLOCK_LIMIT to 8 MiB

On Wed, Nov 24, 2021 at 02:25:09PM +0100, David Hildenbrand wrote:
> On 24.11.21 14:23, Jason Gunthorpe wrote:
> > On Wed, Nov 24, 2021 at 09:57:32AM +0100, David Hildenbrand wrote:
> > 
> >> Unfortunately it will only be a band aid AFAIU. I can rewrite my
> >> reproducer fairly easily to pin the whole 2M range first, pin a second
> >> time only a single page, and then unpin the 2M range, resulting in the
> >> very same way to block THP. (I can block some THP less because I always
> >> need the possibility to memlock 2M first, though).
> > 
> > Oh!
> > 
> > The issue is GUP always pins an entire compound, no matter how little
> > the user requests.
> 
> That's a different issue. I make sure to split the compound page before
> pinning anything :)

?? Where is that done in GUP?

Jason