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SubjectRe: [PATCH 4/4] block: Optionally snapshot page contents to provide stable pages during write
On Thu, Dec 13, 2012 at 12:08:11AM -0800, Darrick J. Wong wrote:
> diff --git a/mm/bounce.c b/mm/bounce.c
> index 0420867..fa11935 100644
> --- a/mm/bounce.c
> +++ b/mm/bounce.c
> @@ -178,6 +178,38 @@ static void bounce_end_io_read_isa(struct bio *bio, int err)
> __bounce_end_io_read(bio, isa_page_pool, err);
> }
>
> +#ifdef CONFIG_NEED_BOUNCE_POOL
> +static int might_snapshot_stable_page_write(struct bio **bio_orig)
> +{
> + return bio_data_dir(*bio_orig) == WRITE;
> +}
> +
> +static int should_snapshot_stable_pages(struct page *page, int rw)
> +{
> + struct backing_dev_info *bdi;
> + struct address_space *mapping = page_mapping(page);
> +
> + if (!mapping)
> + return 0;
> + bdi = mapping->backing_dev_info;
> + if (!bdi_cap_stable_pages_required(bdi))
> + return 0;
> +
> + return mapping->host->i_sb->s_flags & MS_SNAP_STABLE &&
> + rw == WRITE;
> +}
> +#else
> +static int might_snapshot_stable_page_write(struct bio **bio_orig)
> +{
> + return 0;
> +}
> +
> +static int should_snapshot_static_pages(struct page *page, int rw)
^^^^^^
It should be _stable_.

Regards,
- Zheng
> +{
> + return 0;
> +}
> +#endif /* CONFIG_NEED_BOUNCE_POOL */
> +
> static void __blk_queue_bounce(struct request_queue *q, struct bio **bio_orig,
> mempool_t *pool)
> {
> @@ -192,7 +224,8 @@ static void __blk_queue_bounce(struct request_queue *q, struct bio **bio_orig,
> /*
> * is destination page below bounce pfn?
> */
> - if (page_to_pfn(page) <= queue_bounce_pfn(q))
> + if (page_to_pfn(page) <= queue_bounce_pfn(q) &&
> + !should_snapshot_stable_pages(page, rw))
> continue;
>
> /*
> @@ -284,7 +317,8 @@ void blk_queue_bounce(struct request_queue *q, struct bio **bio_orig)
> * don't waste time iterating over bio segments
> */
> if (!(q->bounce_gfp & GFP_DMA)) {
> - if (queue_bounce_pfn(q) >= blk_max_pfn)
> + if (queue_bounce_pfn(q) >= blk_max_pfn &&
> + !might_snapshot_stable_page_write(bio_orig))
> return;
> pool = page_pool;
> } else {


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