Messages in this thread | | | Subject | Re: [PATCH] btrfs: Disable BTRFS on platforms having 256K pages | From | Christophe Leroy <> | Date | Thu, 10 Jun 2021 16:50:09 +0200 |
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Le 10/06/2021 à 15:54, Chris Mason a écrit : > >> On Jun 10, 2021, at 1:23 AM, Christophe Leroy <christophe.leroy@csgroup.eu> wrote: >> >> With a config having PAGE_SIZE set to 256K, BTRFS build fails >> with the following message >> >> include/linux/compiler_types.h:326:38: error: call to '__compiletime_assert_791' declared with attribute error: BUILD_BUG_ON failed: (BTRFS_MAX_COMPRESSED % PAGE_SIZE) != 0 >> >> BTRFS_MAX_COMPRESSED being 128K, BTRFS cannot support platforms with >> 256K pages at the time being. >> >> There are two platforms that can select 256K pages: >> - hexagon >> - powerpc >> >> Disable BTRFS when 256K page size is selected. >> > > We’ll have other subpage blocksize concerns with 256K pages, but this BTRFS_MAX_COMPRESSED #define is arbitrary. It’s just trying to have an upper bound on the amount of memory we’ll need to uncompress a single page’s worth of random reads. > > We could change it to max(PAGE_SIZE, 128K) or just bump to 256K. >
But if 256K is problematic in other ways, is it worth bumping BTRFS_MAX_COMPRESSED to 256K ?
David, in below mail, said that 256K support would require deaper changes. So disabling BTRFS support seems the easiest solution for the time being, at least for Stable (I forgot the Fixes: tag and the CC: to stable).
On powerpc, 256k pages is a corner case, it requires customised binutils, so I don't think disabling BTRFS is a issue there. For hexagon I don't know.
https://lkml.org/lkml/2021/6/9/978
Le 09/06/2021 à 17:22, David Sterba a écrit : > On Wed, Jun 09, 2021 at 04:01:20PM +0200, Christophe Leroy wrote: >> Le 09/06/2021 à 15:55, kernel test robot a écrit : >>> tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master >>> head: 368094df48e680fa51cedb68537408cfa64b788e >>> commit: 4eeef098b43242ed145c83fba9989d586d707589 powerpc/44x: Remove STDBINUTILS kconfig option >>> date: 4 months ago >>> config: powerpc-randconfig-r012-20210609 (attached as .config) >>> compiler: powerpc-linux-gcc (GCC) 9.3.0 >> >> That's a BTRFS issue, and not directly linked to the above mentioned commit. Before that commit the >> problem was already present. >> >> Problem is that with 256k PAGE_SIZE, following BUILD_BUG() pops up: >> >> BUILD_BUG_ON((BTRFS_MAX_COMPRESSED % PAGE_SIZE) != 0) > > A 256K page is a problem for btrfs, until now I was not even aware > there's an architecture supporting that so. That the build fails is > probably best thing. Maximum metadata nodesize supported is 64K and > having that on a 256K page would need deeper changes, no top of the > currently developed subpage changes (that do 4K blocks on 64K pages). >
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