On Tue, Dec 08, 2020 at 08:51:45AM +0900, Daeho Jeong wrote: > > I am trying to review this but it is very hard, as the f2fs compression > > code is > > very hard to understand. > > > > It looks like a 'struct decompress_io_ctx' represents the work to > > decompress a > > particular cluster. Since the compressed data of the cluster can be read > > using > > multiple bios, there is a reference count of how many pages are remaining > > to be > > read before all the cluster's pages have been read and decompression can > > start. > > > > What I don't understand is why that reference counting needs to work > > differently > > depending on whether verity is enabled or not. Shouldn't it be exactly the > > same? > > > > There also seems to be some confusion about the scope of STEP_VERITY. > > Before > > f2fs compression was added, it was a per-bio thing. But now in a compressed > > file, it's really a per-cluster thing, since all decompressed pages in a > > compressed cluster are verified (or not verified) at once. > > > > Wouldn't it make a lot more sense to, when a cluster needs both compression > > and > > verity, *not* set STEP_VERITY on the bios, but rather set a similar flag in > > the > > decompress_io_ctx? > > > > Eric, > > Decompression and verity can be executed in different thread contexts > in different timing, so we need separate counts for each. > > We already use STEP_VERITY for non-compression case, so I think using > this flag in here looks more making sense. > > Thanks,
That didn't really answer my questions. I gave up trying to review this patch as the compression post-read handling is just way too weird and hard to understand. I wrote a patch to clean it all up instead, please take a look: https://lkml.kernel.org/r/20201208060328.2237091-1-ebigg...@kernel.org - Eric
