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

[Zach Brown]

> 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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