Re: [PATCH v6 5/8] fs: xfs: replace BIO_MAX_SECTORS with BIO_MAX_PAGES

From: Ming Lei
Date: Wed Jun 01 2016 - 23:32:57 EST


On Wed, Jun 1, 2016 at 9:48 PM, Christoph Hellwig <hch@xxxxxxxxxxxxx> 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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