From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Chris Mason <clm@fb.com>
Cc: Josef Bacik <josef@toxicpanda.com>,
David Sterba <dsterba@suse.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
linux-btrfs <linux-btrfs@vger.kernel.org>,
"linux-hexagon@vger.kernel.org" <linux-hexagon@vger.kernel.org>
Subject: Re: [PATCH] btrfs: Disable BTRFS on platforms having 256K pages
Date: Thu, 10 Jun 2021 16:50:09 +0200 [thread overview]
Message-ID: <cdadf66e-0a6e-4efe-0326-7236c43b2735@csgroup.eu> (raw)
In-Reply-To: <185278AF-1D87-432D-87E9-C86B3223113E@fb.com>
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).
>
WARNING: multiple messages have this Message-ID (diff)
From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Chris Mason <clm@fb.com>
Cc: "linux-hexagon@vger.kernel.org" <linux-hexagon@vger.kernel.org>,
Josef Bacik <josef@toxicpanda.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
David Sterba <dsterba@suse.com>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
linux-btrfs <linux-btrfs@vger.kernel.org>
Subject: Re: [PATCH] btrfs: Disable BTRFS on platforms having 256K pages
Date: Thu, 10 Jun 2021 16:50:09 +0200 [thread overview]
Message-ID: <cdadf66e-0a6e-4efe-0326-7236c43b2735@csgroup.eu> (raw)
In-Reply-To: <185278AF-1D87-432D-87E9-C86B3223113E@fb.com>
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).
>
next prev parent reply other threads:[~2021-06-10 14:50 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-10 5:23 [PATCH] fs: btrfs: Disable BTRFS on platforms having 256K pages Christophe Leroy
2021-06-10 5:23 ` Christophe Leroy
2021-06-10 13:54 ` [PATCH] " Chris Mason
2021-06-10 13:54 ` Chris Mason
2021-06-10 14:50 ` Christophe Leroy [this message]
2021-06-10 14:50 ` Christophe Leroy
2021-06-10 16:20 ` David Sterba
2021-06-10 16:20 ` David Sterba
2021-06-11 12:58 ` Chris Mason
2021-06-11 12:58 ` Chris Mason
2021-06-11 13:21 ` David Sterba
2021-06-11 13:21 ` David Sterba
2021-06-11 16:56 ` Chris Mason
2021-06-11 16:56 ` Chris Mason
2021-06-12 14:44 ` Brian Cain
2021-06-12 14:44 ` Brian Cain
2021-06-11 12:34 ` [PATCH] fs: " David Sterba
2021-06-11 12:34 ` David Sterba
2021-06-11 13:47 ` Qu Wenruo
2021-06-11 13:47 ` Qu Wenruo
2022-01-04 23:32 ` Qu Wenruo
2022-01-04 23:32 ` Qu Wenruo
2022-01-06 16:31 ` Neal Gompa
2022-01-06 16:31 ` Neal Gompa
2022-01-07 0:13 ` Qu Wenruo
2022-01-07 0:13 ` Qu Wenruo
2022-01-07 2:45 ` Hector Martin
2022-01-07 2:45 ` Hector Martin
2022-01-07 4:55 ` Michael Ellerman
2022-01-07 4:55 ` Michael Ellerman
2022-01-07 5:21 ` Qu Wenruo
2022-01-07 5:21 ` Qu Wenruo
2022-01-10 8:29 ` Christophe Leroy
2022-01-10 8:29 ` Christophe Leroy
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