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Date: Tue, 25 Oct 2016 15:54:31 +0300
From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Christoph Hellwig <hch@infradead.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        "Theodore Ts'o" <tytso@mit.edu>,
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Subject: Re: [PATCHv4 18/43] block: define BIO_MAX_PAGES to HPAGE_PMD_NR if
 huge page cache enabled
Message-ID: <20161025125431.GA22787@node.shutemov.name>
References: <20161025001342.76126-1-kirill.shutemov@linux.intel.com>
 <20161025001342.76126-19-kirill.shutemov@linux.intel.com>
 <20161025072122.GA21708@infradead.org>
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On Tue, Oct 25, 2016 at 12:21:22AM -0700, Christoph Hellwig wrote:
> On Tue, Oct 25, 2016 at 03:13:17AM +0300, Kirill A. Shutemov wrote:
> > We are going to do IO a huge page a time. So we need BIO_MAX_PAGES to be
> > at least HPAGE_PMD_NR. For x86-64, it's 512 pages.
> 
> NAK.  The maximum bio size should not depend on an obscure vm config,
> please send a standalone patch increasing the size to the block list,
> with a much long explanation.  Also you can't simply increase the size
> of the largers pool, we'll probably need more pools instead, or maybe
> even implement a similar chaining scheme as we do for struct
> scatterlist.

The size of required pool depends on architecture: different architectures
has different (huge page size)/(base page size).

Would it be okay if I add one more pool with size equal to HPAGE_PMD_NR,
if it's bigger than than BIO_MAX_PAGES and huge pages are enabled?

-- 
 Kirill A. Shutemov