From: "Kirill A. Shutemov" <kirill@shutemov.name>
Subject: Re: [PATCHv4 18/43] block: define BIO_MAX_PAGES to HPAGE_PMD_NR if
 huge page cache enabled
Date: Tue, 25 Oct 2016 15:54:31 +0300
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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Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Theodore Ts'o <tytso@mit.edu>,
	Andreas Dilger <adilger.kernel@dilger.ca>, Jan Kara <jack@suse.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Hugh Dickins <hughd@google.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Matthew Wilcox <willy@infradead.org>,
	Ross Zwisler <ross.zwisler@linux.intel.com>,
	linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-block@vger.kernel.org
To: Christoph Hellwig <hch@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

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