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From: Wang Yugui <wangyugui@e16-tech.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org,
	Dave Chinner <david@fromorbit.com>,
	Christoph Hellwig <hch@infradead.org>,
	"Darrick J . Wong" <djwong@kernel.org>
Subject: Re: [PATCH 1/3] filemap: Allow __filemap_get_folio to allocate large folios
Date: Sun, 21 May 2023 10:04:35 +0800	[thread overview]
Message-ID: <20230521100434.716E.409509F4@e16-tech.com> (raw)
In-Reply-To: <ZGl6UZ0a+fIAPmn5@casper.infradead.org>

Hi,

> On Sun, May 21, 2023 at 09:02:36AM +0800, Wang Yugui wrote:
> > > +static inline unsigned fgp_order(size_t size)
> > > +{
> > > +	unsigned int shift = ilog2(size);
> > > +
> > > +	if (shift <= PAGE_SHIFT)
> > > +		return 0;
> > > +	return (shift - PAGE_SHIFT) << 26;
> > 
> > int overflow will happen when size > 0.5M(2**19)?
> 
> I don't see it?
> 
> size == 1 << 20;
> 
> shift = 20;
> return (20 - 12) << 26;
> 
> Looks like about 1 << 29 to me.

sorry that I wrongly
1) wrongly conside PAGE_SHIFT as 13 from arch/alpha/include/asm/page.h
it should be 12 from arch/x86/include/asm/page_types.h.

2) wrongly conside
	(20 - 12) << 26
as
	1<< (20 - 12) << 26

Best Regards
Wang Yugui (wangyugui@e16-tech.com)
2023/05/21



  reply	other threads:[~2023-05-21  2:14 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-05-20 16:36 [PATCH 0/3] Create large folios in iomap buffered write path Matthew Wilcox (Oracle)
2023-05-20 16:36 ` [PATCH 1/3] filemap: Allow __filemap_get_folio to allocate large folios Matthew Wilcox (Oracle)
2023-05-21  1:02   ` Wang Yugui
2023-05-21  1:56     ` Matthew Wilcox
2023-05-21  2:04       ` Wang Yugui [this message]
2023-05-21  3:39         ` Matthew Wilcox
2023-05-21  2:13   ` Dave Chinner
2023-05-21  3:38     ` Matthew Wilcox
2023-05-23  5:59   ` Christoph Hellwig
2023-05-23 12:17     ` Matthew Wilcox
2023-05-20 16:36 ` [PATCH 2/3] iomap: Create large folios in the buffered write path Matthew Wilcox (Oracle)
2023-05-20 16:36 ` [PATCH 3/3] iomap: Copy larger chunks from userspace Matthew Wilcox (Oracle)
2023-05-20 19:11   ` kernel test robot
2023-05-20 19:25   ` kernel test robot
2023-05-21  0:49 ` [PATCH 0/3] Create large folios in iomap buffered write path Wang Yugui
2023-05-21  0:59   ` Matthew Wilcox
2023-05-21  1:38     ` Wang Yugui
2023-05-21  2:49 ` Dave Chinner
2023-05-21 11:40 ` Wang Yugui
2023-05-31  4:34   ` Wang Yugui

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