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From: Ming Lei <tom.leiming@gmail.com>
Date: Wed, 26 Oct 2016 15:30:05 +0800
Message-ID: <CACVXFVOYXJW1c8LHiwoM9a0nLnkeeGVPUZRvs2=MohFwvhugsQ@mail.gmail.com>
Subject: Re: [PATCHv4 18/43] block: define BIO_MAX_PAGES to HPAGE_PMD_NR if
 huge page cache enabled
To: Andreas Dilger <adilger@dilger.ca>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
        Christoph Hellwig <hch@infradead.org>,
        "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 FS Devel <linux-fsdevel@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>,
        linux-block <linux-block@vger.kernel.org>
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On Wed, Oct 26, 2016 at 12:13 PM, Andreas Dilger <adilger@dilger.ca> wrote:
> On Oct 25, 2016, at 6:54 AM, Kirill A. Shutemov <kirill@shutemov.name> wrote:
>>
>> 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?
>
> Why wouldn't you have all the pool sizes in between?  Definitely 1MB has
> been too small already for high-bandwidth IO.  I wouldn't mind BIOs up to
> 4MB or larger since most high-end RAID hardware does best with 4MB IOs.

I am preparing for the multipage bvec support[1], and once it is ready the
default 256 bvecs should be enough for normal cases.

I will post them out next month for review.

[1] https://github.com/ming1/linux/tree/mp-bvec-0.1-v4.9

Thanks,
Ming

>
> Cheers, Andreas
>
>
>
>
>


-- 
Ming Lei