On 12/07, Eric Biggers wrote: > 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, I also tried to review your patch, but it's quite hard to follow quickly and requires stress tests for a while. Given upcoming merge window and urgency of the bug, let me apply Daeho's fix first. By any chance, may I ask revisiting your clean-up on top of the fix in the next cycle? Thanks, > > - Eric
