Re: [PATCH 02/11] io_uring: get rid of remap_pfn_range() for mapping rings/sqes

[Gabriel Krisman Bertazi <krisman@suse.de>]

Jens Axboe <axboe@kernel.dk> writes:

> Rather than use remap_pfn_range() for this and manually free later,
> switch to using vm_insert_pages() and have it Just Work.
>
> If possible, allocate a single compound page that covers the range that
> is needed. If that works, then we can just use page_address() on that
> page. If we fail to get a compound page, allocate single pages and use
> vmap() to map them into the kernel virtual address space.
>
> This just covers the rings/sqes, the other remaining user of the mmap
> remap_pfn_range() user will be converted separately. Once that is done,
> we can kill the old alloc/free code.
>
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> ---
>  io_uring/io_uring.c | 136 +++++++++++++++++++++++++++++++++++++++++---
>  io_uring/io_uring.h |   2 +
>  2 files changed, 130 insertions(+), 8 deletions(-)
>
> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
> index 104899522bc5..982545ca23f9 100644
> --- a/io_uring/io_uring.c
> +++ b/io_uring/io_uring.c
> @@ -2594,6 +2594,33 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
>  	return READ_ONCE(rings->cq.head) == READ_ONCE(rings->cq.tail) ? ret : 0;
>  }
>  
> +static void io_pages_unmap(void *ptr, struct page ***pages,
> +			   unsigned short *npages)
> +{
> +	bool do_vunmap = false;
> +
> +	if (*npages) {
> +		struct page **to_free = *pages;
> +		int i;
> +
> +		/*
> +		 * Only did vmap for the non-compound multiple page case.
> +		 * For the compound page, we just need to put the head.
> +		 */
> +		if (PageCompound(to_free[0]))
> +			*npages = 1;
> +		else if (*npages > 1)
> +			do_vunmap = true;
> +		for (i = 0; i < *npages; i++)
> +			put_page(to_free[i]);
> +	}

Hi Jens,

wouldn't it be simpler to handle the compound case separately as a
folio?  Then you folio_put the compound page here and just handle the
non-continuous case after.

-- 
Gabriel Krisman Bertazi