netdev - Re: [PATCH v2 01/34] mm/gup: add make_dirty arg to put_user_pages_dirty

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Date:   Tue, 6 Aug 2019 13:39:16 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Ira Weiny <ira.weiny@...el.com>, <john.hubbard@...il.com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Jan Kara <jack@...e.cz>, Jason Gunthorpe <jgg@...pe.ca>,
        Jérôme Glisse <jglisse@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        <amd-gfx@...ts.freedesktop.org>, <ceph-devel@...r.kernel.org>,
        <devel@...verdev.osuosl.org>, <devel@...ts.orangefs.org>,
        <dri-devel@...ts.freedesktop.org>,
        <intel-gfx@...ts.freedesktop.org>, <kvm@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-block@...r.kernel.org>, <linux-crypto@...r.kernel.org>,
        <linux-fbdev@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
        <linux-media@...r.kernel.org>, <linux-mm@...ck.org>,
        <linux-nfs@...r.kernel.org>, <linux-rdma@...r.kernel.org>,
        <linux-rpi-kernel@...ts.infradead.org>,
        <linux-xfs@...r.kernel.org>, <netdev@...r.kernel.org>,
        <rds-devel@....oracle.com>, <sparclinux@...r.kernel.org>,
        <x86@...nel.org>, <xen-devel@...ts.xenproject.org>,
        Christoph Hellwig <hch@....de>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v2 01/34] mm/gup: add make_dirty arg to
 put_user_pages_dirty_lock()

On 8/6/19 10:39 AM, Ira Weiny wrote:
> On Sun, Aug 04, 2019 at 03:48:42PM -0700, john.hubbard@...il.com wrote:
>> From: John Hubbard <jhubbard@...dia.com>
...
>> -
>>  /**
>> - * put_user_pages_dirty() - release and dirty an array of gup-pinned pages
>> - * @pages:  array of pages to be marked dirty and released.
>> + * put_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages
>> + * @pages:  array of pages to be maybe marked dirty, and definitely released.
> 
> Better would be.
> 
> @pages:  array of pages to be put

OK, I'll change to that wording.

> 
>>   * @npages: number of pages in the @pages array.
>> + * @make_dirty: whether to mark the pages dirty
>>   *
>>   * "gup-pinned page" refers to a page that has had one of the get_user_pages()
>>   * variants called on that page.
>>   *
>>   * For each page in the @pages array, make that page (or its head page, if a
>> - * compound page) dirty, if it was previously listed as clean. Then, release
>> - * the page using put_user_page().
>> + * compound page) dirty, if @make_dirty is true, and if the page was previously
>> + * listed as clean. In any case, releases all pages using put_user_page(),
>> + * possibly via put_user_pages(), for the non-dirty case.
> 
> I don't think users of this interface need this level of detail.  I think
> something like.
> 
>  * For each page in the @pages array, release the page.  If @make_dirty is
>  * true, mark the page dirty prior to release.

Yes, it is too wordy, I'll change to that.

> 
...
>> -void put_user_pages_dirty_lock(struct page **pages, unsigned long npages)
>> -{
>> -	__put_user_pages_dirty(pages, npages, set_page_dirty_lock);
>> +	/*
>> +	 * TODO: this can be optimized for huge pages: if a series of pages is
>> +	 * physically contiguous and part of the same compound page, then a
>> +	 * single operation to the head page should suffice.
>> +	 */
> 
> I think this comment belongs to the for loop below...  or just something about
> how to make this and put_user_pages() more efficient.  It is odd, that this is
> the same comment as in put_user_pages()...

Actually I think I'll just delete the comment entirely, it's just noise really.

> 
> The code is good.  So... Other than the comments.
> 
> Reviewed-by: Ira Weiny <ira.weiny@...el.com>


Thanks for the review!


thanks,
-- 
John Hubbard
NVIDIA