On 1/1/23 08:18, Hillf Danton wrote:
> Subject:
> Re: [PATCH v2 17/21] block, blksnap: snapshot image block device
> From:
> Hillf Danton <hdanton@xxxxxxxx>
> Date:
> 1/1/23, 08:18
>
> To:
> Sergei Shtepa <sergei.shtepa@xxxxxxxxx>
> CC:
> "axboe@xxxxxxxxx" <axboe@xxxxxxxxx>, "corbet@xxxxxxx" <corbet@xxxxxxx>, "linux-mm@xxxxxxxxx" <linux-mm@xxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>
>
>
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> hdanton@xxxxxxxx, please exercise caution when clicking on links or opening
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>
>
> On 9 Dec 2022 15:23:27 +0100 Sergei Shtepa
> > Provides the operation of block devices of snapshot images. Read and
> > write operations are redirected to the regions of difference blocks for
> > block device (struct diff_area).
> >
> > Signed-off-by: Sergei Shtepa
> > ---
>
> Thanks for your patchset.
Thanks for the review.
>
> > +static int snapimage_kthread_worker_fn(void *param)
> > +{
> > + struct snapimage *snapimage = param;
> > + struct bio *bio;
> > + int ret = 0;
> > +
> > + while (!kthread_should_stop()) {
> > + bio = get_bio_from_queue(snapimage);
> > + if (!bio) {
> > + schedule_timeout_interruptible(HZ / 100);
> > + continue;
> > + }
>
> Given the wake_up_process() below, s$HZ / 100$HZ * 1000$ to avoid
> unnecessary wakeups [1].
>
> And because of no signal handling added, use schedule_timeout_idle() instead.
Yes, this function will be rewritten to eliminate unnecessary wake-ups.
The code that Christoph proposed in the letter at Dec 15 should work well.
>
> [1]
> https://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flkml%2F20210419085027.761150-2-elver%40google.com%2F&data=05%7C01%7Csergei.shtepa%40veeam.com%7C765d591d47ad4d93857208daebc92508%7Cba07baab431b49edadd7cbc3542f5140%7C1%7C1%7C638081546440884849%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=rbINOq7m31DFhjHLnQKFHQuoWB64ZhmnWbAVLuNwv7w%3D&reserved=0
>
> > +
> > + snapimage_process_bio(snapimage, bio);
> > + }
> > +
> > + while ((bio = get_bio_from_queue(snapimage)))
> > + snapimage_process_bio(snapimage, bio);
> > +
> > + return ret;
> > +}
> > +
> > +static void snapimage_submit_bio(struct bio *bio)
> > +{
> > + struct snapimage *snapimage = bio->bi_bdev->bd_disk->private_data;
> > + gfp_t gfp = GFP_NOIO;
> > +
> > + if (bio->bi_opf & REQ_NOWAIT)
> > + gfp |= GFP_NOWAIT;
> > + if (snapimage->is_ready) {
> > + spin_lock(&snapimage->queue_lock);
> > + bio_list_add(&snapimage->queue, bio);
> > + spin_unlock(&snapimage->queue_lock);
> > +
> > + wake_up_process(snapimage->worker);
> > + } else
> > + bio_io_error(bio);
> > +}
>
