Am 19.04.2021 um 11:13 hat Peter Lieven geschrieben: > > > > Am 19.04.2021 um 10:36 schrieb Peter Lieven <p...@kamp.de>: > > > > > > > >> Am 15.04.2021 um 17:22 schrieb Kevin Wolf <kw...@redhat.com>: > >> > >> Peter, three years ago you changed 'qemu-img convert' to sacrifice some > >> sparsification in order to get aligned requests on the target image. At > >> the time, I thought the impact would be small, but it turns out that > >> this can end up wasting gigabytes of storagee (like converting a fully > >> zeroed 10 GB image taking 2.8 GB instead of a few kilobytes). > >> > >> https://bugzilla.redhat.com/show_bug.cgi?id=1882917 > >> > >> I'm not entirely sure how to attack this best since this is a tradeoff, > >> but maybe the approach in this series is still good enough for the case > >> that you wanted to fix back then? > >> > >> Of course, it would be possible to have a more complete fix like looking > >> forward a few blocks more before writing data, but that would probably > >> not be entirely trivial because you would have to merge blocks with ZERO > >> block status with DATA blocks that contain only zeros. I'm not sure if > >> it's worth this complication of the code. > > > > I will try to look into this asap. > > Besides from the reproducer described in the ticket, I retried my old > conversion test in our environment: > > Before commit 8dcd3c9b91: reads 4608 writes 14959 > After commit 8dcd3c9b91: reads 0 writes 14924 > With Kevins patch: reads 110 writes 14924 > > I think this is a good result if it avoids other issues.
Sounds like a promising way to make the tradeoff. Thanks for testing! Kevin
