linux-kernel - Re: memfill

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Message-ID: <20170207172258.GM2267@bombadil.infradead.org>
Date:   Tue, 7 Feb 2017 09:22:58 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        sergey.senozhatsky@...il.com, iamjoonsoo.kim@....com,
        ngupta@...are.org, zhouxianrong@...wei.com, zhouxiyu@...wei.com,
        weidu.du@...wei.com, zhangshiming5@...wei.com,
        Mi.Sophia.Wang@...wei.com, won.ho.park@...wei.com
Subject: Re: memfill

On Tue, Feb 07, 2017 at 09:40:04AM +0000, David Howells wrote:
> Matthew Wilcox <willy@...radead.org> wrote:
> 
> > [adding linux-arch to see if anyone there wants to do an optimised
> > version of memfill for their CPU]
> 
> For mn10300, this is superfluous since the memset() implementation will do
> optimised filling of up to 8 x 4 bytes per loop if the alignments suit.
> 
> This is also superfluous for frv as that will do up to 8 x 8 bytes per loop.
> 
> So on both those arches, memfill() should probably just wrap memset().

You've misunderstood the purpose of memfill.  memfill allows the caller
to specify a pattern which is not a single byte in size, eg memfill(addr,
0x12345678, 64) would result in 0x12345678 being reproduced 16 times.
memset(addr, 0x12345678, 64) would result in 0x78 being reproduced
64 times.