On Wed, Dec 09, 2020 at 09:34:06AM +0800, Chao Yu wrote: > On 2020/12/9 7:55, Jaegeuk Kim wrote: > > 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 > > Me too, it needs more time to check whether the cleanup doesn't miss any > cases. > > Thanks, > > > 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,
I'm not in a hurry, please just take a look when you have time. - Eric
