From: Daeho Jeong <email@example.com> To: Eric Biggers <firstname.lastname@example.org> Cc: email@example.com, firstname.lastname@example.org, email@example.com, Daeho Jeong <firstname.lastname@example.org> Subject: Re: [f2fs-dev] [PATCH] f2fs: change fiemap way in printing compression chunk Date: Wed, 21 Jul 2021 18:04:22 -0700 [thread overview] Message-ID: <CACOAw_xeTSa8J_9=+6thXvFT75u734D5asNRogUxt+DC-tPhxg@mail.gmail.com> (raw) In-Reply-To: <YPi4rRg2ZPFBWaTZ@sol.localdomain> On Wed, Jul 21, 2021 at 5:15 PM Eric Biggers <email@example.com> wrote: > > On Wed, Jul 21, 2021 at 03:30:46PM -0700, Daeho Jeong wrote: > > Hi Eric, > > > > On Wed, Jul 21, 2021 at 2:35 PM Eric Biggers <firstname.lastname@example.org> wrote: > > > > > > On Wed, Jul 21, 2021 at 12:20:48AM -0700, Daeho Jeong wrote: > > > > From: Daeho Jeong <email@example.com> > > > > > > > > When we print out a discontinuous compression chunk, it shows like a > > > > continuous chunk now. To show it more correctly, I've changed the way of > > > > printing fiemap info like below. Plus, eliminated NEW_ADDR(-1) in fiemap > > > > info, since it is not in fiemap user api manual. > > > > > > > > 0: 0000000000000000 0000000000000000 0000000000001000 1008 (M/E) > > > > 1: 0000000000001000 0000000f15c0f000 0000000000001000 1008 (M/E) > > > > 2: 0000000000002000 0000000000000000 0000000000002000 1808 (M/U/E) > > > > 3: 0000000000004000 0000000000000000 0000000000001000 1008 (M/E) > > > > 4: 0000000000005000 0000000f15c10000 0000000000001000 1008 (M/E) > > > > 5: 0000000000006000 0000000000000000 0000000000002000 1808 (M/U/E) > > > > 6: 0000000000008000 0000000000000000 0000000000001000 1008 (M/E) > > > > > > Please label these columns. > > > > > > Anyway, this doesn't appear to work quite in the way I had in mind. With this > > > patch, what I'm seeing is: > > > > > > $ head -c 16384 /dev/zero > file; xfs_io -c "fiemap -v" file > > > file: > > > EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS > > > 0: [0..7]: 0..7 8 0x1008 > > > 1: [8..15]: 2683128..2683135 8 0x1008 > > > 2: [16..31]: 0..15 16 0x1809 > > > > > > So, working in 512-byte sectors, the logical sectors 0-31 are stored as one > > > compressed cluster in the 8 physical sectors 2683128-2683135. > > > > > > The problem is, with this patch these physical sectors are reported at logical > > > sectors 8-15 instead of 0-7. Obviously, this isn't particularly well-defined, > > > but I thought it was logical for the physical blocks to be associated with the > > > first logical blocks. That is what the tests I've written (xfstest f2fs/002, > > > and the Android vts_kernel_encryption_test) assume. > > > > > > Is there any particular reason why you wouldn't report instead: > > > > > > 0: [0..7]: 2683128..2683135 8 0x1008 > > > 1: [8..31]: 0..23 8 0x1809 > > > > > > - Eric > > > > The reason is related to how F2FS stores the mapping information in > > the mapping table. > > Actually, the mapping inside of the table is like this. > > [0..7]: COMPR_ADDR flag(0x1008) -> merged, encoded > > [8..15]: 2683128..2683135 flag(0x1008) -> merged, encoded > > [16..31]: NEW_ADDR flag(0x1809) -> merged, unwritten(!), last_extent > > > > I understand what you mean. > > But, if we adapt to your way, how do you think we can print out when > > we ask for f2fs to print out only the [8..15] area? Zero address? How > > about flags? > > I think the current way explains the layout of the f2fs metadata more exactly. > > > > How f2fs stores the mapping information doesn't matter. That's an > implementation detail that shouldn't be exposed to userspace. The only thing > that should be exposed is the actual mapping, and for that it seems natural to > report the physical blocks first. > > There is no perfect solution for how to handle the remaining logical blocks, > given that the fiemap API was not designed for compressed files, but I think we > should just go with extending the length of the last compressed extent in the > cluster to cover the remaining logical blocks, i.e.: > > [0..31]: 2683128..2683159 flag(0x1009) -> merged, encoded, last_extent > > That's what btrfs does on compressed files. > > - Eric I also agree that that's an implementation detail that shouldn't be exposed to userspace. I want to make it more clear for better appearance. Do you think we have to remove "unwritten" information below? I also think it might be unnecessary information for the user. [0..31]: 2683128..2683159 flag(0x1009) -> merged, encoded, last_extent (unwritten?) Do you want f2fs to print out the info on a cluster basis, even when the user asks for one block information? Like If the user asks for the info of [8..15], f2fs will return the info of [0..31]? Thank you,
next prev parent reply other threads:[~2021-07-22 1:04 UTC|newest] Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-07-21 7:20 Daeho Jeong 2021-07-21 21:35 ` [f2fs-dev] " Eric Biggers 2021-07-21 22:30 ` Daeho Jeong 2021-07-22 0:15 ` Eric Biggers 2021-07-22 1:04 ` Daeho Jeong [this message] 2021-07-22 1:15 ` Eric Biggers 2021-07-22 1:40 ` Daeho Jeong 2021-07-22 1:56 ` Eric Biggers 2021-07-22 3:59 ` Daeho Jeong 2021-07-22 6:24 ` Christoph Hellwig 2021-07-22 6:39 ` Daeho Jeong
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