linux-kernel - Re: [PATCH v6 5/8] fs: xfs: replace BIO_MAX_SECTORS with BIO_MAX

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Message-ID: <CACVXFVOJ-RDpu3yy1af3ZTo16-q4J6hsuV5d=6_0fi-i4b3ycw@mail.gmail.com>
Date:	Thu, 2 Jun 2016 11:32:51 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Jens Axboe <axboe@...com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-block@...r.kernel.org, Dave Chinner <david@...morbit.com>,
	"supporter:XFS FILESYSTEM" <xfs@....sgi.com>
Subject: Re: [PATCH v6 5/8] fs: xfs: replace BIO_MAX_SECTORS with BIO_MAX_PAGES

On Wed, Jun 1, 2016 at 9:48 PM, Christoph Hellwig <hch@...radead.org> wrote:
> On Mon, May 30, 2016 at 09:34:33PM +0800, Ming Lei wrote:
>> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
>> index e71cfbd..e5d713b 100644
>> --- a/fs/xfs/xfs_buf.c
>> +++ b/fs/xfs/xfs_buf.c
>> @@ -1157,9 +1157,7 @@ xfs_buf_ioapply_map(
>>
>>  next_chunk:
>>       atomic_inc(&bp->b_io_remaining);
>> -     nr_pages = BIO_MAX_SECTORS >> (PAGE_SHIFT - BBSHIFT);
>> -     if (nr_pages > total_nr_pages)
>> -             nr_pages = total_nr_pages;
>> +     nr_pages = min(total_nr_pages, BIO_MAX_PAGES);
>>
>>       bio = bio_alloc(GFP_NOIO, nr_pages);
>
> While I think this is a useful cleanup on it's own I think
> you'd make everyones life easier if bio_alloc simply clamped down
> the passed nr_pages value to the maximum allowed.

Yes, that looks a good cleanup, but need be careful because the
passed 'nr_pages' can be used after returning from bio_alloc() in
the current function, and it is easy to see this usage.

So we can do that in another patchset instead of this one.

Thanks,

> --
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