Date:   Wed, 24 Nov 2021 09:28:42 -0400
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     David Hildenbrand <david@redhat.com>
Cc:     Vlastimil Babka <vbabka@suse.cz>, Jens Axboe <axboe@kernel.dk>,
        Andrew Dona-Couch <andrew@donacou.ch>,
        Andrew Morton <akpm@linux-foundation.org>,
        Drew DeVault <sir@cmpwn.com>,
        Ammar Faizi <ammarfaizi2@gnuweeb.org>,
        linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
        io_uring Mailing List <io-uring@vger.kernel.org>,
        Pavel Begunkov <asml.silence@gmail.com>, linux-mm@kvack.org
Subject: Re: [PATCH] Increase default MLOCK_LIMIT to 8 MiB
Message-ID: <20211124132842.GH5112@ziepe.ca>
References: <20211123132523.GA5112@ziepe.ca>
 <10ccf01b-f13a-d626-beba-cbee70770cf1@redhat.com>
 <20211123140709.GB5112@ziepe.ca>
 <e4d7d211-5d62-df89-8f94-e49385286f1f@redhat.com>
 <20211123170056.GC5112@ziepe.ca>
 <dd92a69a-6d09-93a1-4f50-5020f5cc59d0@suse.cz>
 <20211123235953.GF5112@ziepe.ca>
 <2adca04f-92e1-5f99-6094-5fac66a22a77@redhat.com>
 <20211124132353.GG5112@ziepe.ca>
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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