linux-kernel - Re: [PATCH 2/6] block: add dio_w_*() wrappers for pin, unpin user pages

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Message-ID: <4c6903d4-0612-5097-0005-4a9420890826@nvidia.com>
Date:   Sat, 27 Aug 2022 16:59:32 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Jens Axboe <axboe@...nel.dk>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Miklos Szeredi <miklos@...redi.hu>,
        Christoph Hellwig <hch@...radead.org>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna@...nel.org>, Jan Kara <jack@...e.cz>,
        Logan Gunthorpe <logang@...tatee.com>,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/6] block: add dio_w_*() wrappers for pin, unpin user
 pages

On 8/27/22 15:27, Andrew Morton wrote:
>> +static inline void dio_w_unpin_user_pages(struct page **pages,
>> +					  unsigned long npages)
>> +{
>> +	unsigned long i;
>> +
>> +	for (i = 0; i < npages; i++)
>> +		put_page(pages[i]);
>> +}
> 
> release_pages()?  Might be faster if many of the pages are page_count()==1.

Sure. I was being perhaps too cautious about changing too many things
at once, earlier when I wrote this. 

> 
> (release_pages() was almost as simple as the above when I added it a
> million years ago.  But then progress happened).
> 

Actually, I'm tempted update the release_pages() API as well, because it
uses an int for npages, while other things (in gup.c, anyway) are moving
over to unsigned long.

Anyway, I'll change my patch locally for now, to this:

static inline void dio_w_unpin_user_pages(struct page **pages,
					  unsigned long npages)
{
	/* Careful, release_pages() uses a smaller integer type for npages: */
	if (WARN_ON_ONCE(npages > (unsigned long)INT_MAX))
		return;

	release_pages(pages, (int)npages);
}

...in hopes that I can somehow find a way to address Al Viro's other
comments, which have the potential to doom the whole series, heh.


thanks,

-- 
John Hubbard
NVIDIA