From: Matthew Wilcox <willy@infradead.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Hugh Dickins <hughd@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Chuck Lever III <chuck.lever@oracle.com>,
Mark Hemment <markhemm@googlemail.com>,
Patrice CHOTARD <patrice.chotard@foss.st.com>,
Mikulas Patocka <mpatocka@redhat.com>,
Lukas Czerner <lczerner@redhat.com>,
"Darrick J. Wong" <djwong@kernel.org>,
"Jason A. Donenfeld" <Jason@zx2c4.com>,
Borislav Petkov <bp@alien8.de>,
linux-mm@kvack.org, linux-nfs@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-stm32@st-md-mailman.stormreply.com,
viro@zeniv.linux.org.uk, x86@kernel.org
Subject: Re: making x86 clear_user not suck, was Re: [PATCH] tmpfs: fix regressions from wider use of ZERO_PAGE
Date: Wed, 13 Apr 2022 19:06:06 +0100 [thread overview]
Message-ID: <YlcRDrEGwEz1EymZ@casper.infradead.org> (raw)
In-Reply-To: <20220412045757.GA5131@lst.de>
On Tue, Apr 12, 2022 at 06:57:57AM +0200, Christoph Hellwig wrote:
> On Fri, Apr 08, 2022 at 11:08:29PM -0700, Hugh Dickins wrote:
> > >
> > > Either way I'd rather do this optimization in iov_iter_zero rather
> > > than hiding it in tmpfs.
> >
> > Let's see what others say. I think we would all prefer clear_user() to be
> > enhanced, and hack around it neither here in tmpfs nor in iov_iter_zero().
> > But that careful work won't get done by magic, nor by me.
>
> I agree with that.
>
> > And iov_iter_zero() has to deal with a wider range of possibilities,
> > when pulling in cache lines of ZERO_PAGE(0) will be less advantageous,
> > than in tmpfs doing a large dd - the case I'm aiming not to regress here
> > (tmpfs has been copying ZERO_PAGE(0) like this for years).
>
> Maybe. OTOH I'd hate to have iov_iter_zero not used much because it
> sucks too much.
>
> So how can we entice someone with the right knowledge to implement a
> decent clear_user for x86?
Apparently that already happened, but it needs finishing up:
https://lore.kernel.org/lkml/Yk9yBcj78mpXOOLL@zx2c4.com/
next prev parent reply other threads:[~2022-04-13 18:06 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-08 20:38 Hugh Dickins
2022-04-09 5:06 ` Christoph Hellwig
2022-04-09 6:08 ` Hugh Dickins
2022-04-12 4:57 ` making x86 clear_user not suck, was " Christoph Hellwig
2022-04-13 18:06 ` Matthew Wilcox [this message]
2022-04-12 23:22 ` Andrew Morton
2022-04-13 16:41 ` Christoph Hellwig
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