linux-kernel - Re: [WiP]: aio support for migrating pages (Re: [PATCH V2 1/2] mm: hotplug: implement non-movable version of get_user_pages() called get_user_pages_non

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Message-ID: <20130517181708.GG318@lenny.home.zabbo.net>
Date:	Fri, 17 May 2013 11:17:08 -0700
From:	Zach Brown <zab@...hat.com>
To:	Benjamin LaHaise <bcrl@...ck.org>
Cc:	Tang Chen <tangchen@...fujitsu.com>, Mel Gorman <mgorman@...e.de>,
	Minchan Kim <minchan@...nel.org>,
	Lin Feng <linfeng@...fujitsu.com>, akpm@...ux-foundation.org,
	viro@...iv.linux.org.uk, khlebnikov@...nvz.org, walken@...gle.com,
	kamezawa.hiroyu@...fujitsu.com, riel@...hat.com,
	rientjes@...gle.com, isimatu.yasuaki@...fujitsu.com,
	wency@...fujitsu.com, laijs@...fujitsu.com, jiang.liu@...wei.com,
	jmoyer@...hat.com, linux-mm@...ck.org, linux-aio@...ck.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [WiP]: aio support for migrating pages (Re: [PATCH V2 1/2] mm:
 hotplug: implement non-movable version of get_user_pages() called
 get_user_pages_non_movable())

> I ended up working on this a bit today, and managed to cobble together 
> something that somewhat works -- please see the patch below.

Just some quick observations:

> +	ctx->ctx_file = anon_inode_getfile("[aio]", &aio_ctx_fops, ctx, O_RDWR);
> +	if (IS_ERR(ctx->ctx_file)) {
> +		ctx->ctx_file = NULL;
> +		return -EAGAIN;
> +	}

It's too bad that aio contexts will now be accounted against the filp
limits (get_empty_filp -> files_stat.max_files, etc). 

> +	for (i=0; i<nr_pages; i++) {
> +		struct page *page;
> +		void *ptr;
> +		page = find_or_create_page(ctx->ctx_file->f_inode->i_mapping,
> +					   i, GFP_KERNEL);
> +		if (!page) {
> +			break;
> +		}
> +		ptr = kmap(page);
> +		clear_page(ptr);
> +		kunmap(page);
> +		SetPageUptodate(page);
> +		SetPageDirty(page);
> +		unlock_page(page);
> +	}

If they're GFP_KERNEL then you don't need to kmap them.  But we probably
want to allocate with GFP_HIGHUSER and then use clear_user_highpage() to
zero them?

- z
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