From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Minchan Kim <minchan@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: clear_page, copy_page address align question?
Date: Tue, 11 Apr 2017 13:12:24 +1000 [thread overview]
Message-ID: <1491880344.4166.224.camel@kernel.crashing.org> (raw)
In-Reply-To: <20170411030823.GB6545@bbox>
On Tue, 2017-04-11 at 12:08 +0900, Minchan Kim wrote:
> Hello,
>
> When I tested zram in ppc64, I got random corruption.
> With investigation, it seems clear_page corrupted the memory.
> I passed 64K kmalloced(kmalloc(PAGE_SIZE)) address to clear_page
> and turned on slub debug so address is not aligned with PAGE_SIZE.
> Is it a valid usecase that non-PAGE_SIZE aligned address is
> used for clear_page in ppc64?
>
> As well, copy_page have same rule, too?
>
> Anyway, when I changed clear_page to memset, it seems the problem
> is gone.
Yes, both clear_page and copy_page assume a PAGE_SHIFT alignment and
are highly optimize according to this.
I wouldn't be surprised of other architectures implementations are the
same.
I don't think it's ever legit to call these functions for something
that isn't a naturally aligned page.
Cheers,
Ben.
next prev parent reply other threads:[~2017-04-11 3:12 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-11 3:08 clear_page, copy_page address align question? Minchan Kim
2017-04-11 3:12 ` Benjamin Herrenschmidt [this message]
2017-04-11 3:21 ` Minchan Kim
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