From: David Sterba <dsterba@suse.cz>
To: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Chris Mason <clm@fb.com>, 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 18:20:46 +0200 [thread overview]
Message-ID: <20210610162046.GB28158@suse.cz> (raw)
In-Reply-To: <cdadf66e-0a6e-4efe-0326-7236c43b2735@csgroup.eu>
On Thu, Jun 10, 2021 at 04:50:09PM +0200, Christophe Leroy wrote:
>
>
> 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.
That it blew up due to the max compressed size is a coincidence. We
could have explicit BUILD_BUG_ONs for page size or other constraints
derived from the page size like INLINE_EXTENT_BUFFER_PAGES.
And there's no such thing like "just bump BTRFS_MAX_COMPRESSED to 256K".
The constant is part of on-disk format for lzo and otherwise changing it
would impact performance so this would need proper evaluation.
WARNING: multiple messages have this Message-ID (diff)
From: David Sterba <dsterba@suse.cz>
To: Christophe Leroy <christophe.leroy@csgroup.eu>
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>,
Chris Mason <clm@fb.com>, 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 18:20:46 +0200 [thread overview]
Message-ID: <20210610162046.GB28158@suse.cz> (raw)
In-Reply-To: <cdadf66e-0a6e-4efe-0326-7236c43b2735@csgroup.eu>
On Thu, Jun 10, 2021 at 04:50:09PM +0200, Christophe Leroy wrote:
>
>
> 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.
That it blew up due to the max compressed size is a coincidence. We
could have explicit BUILD_BUG_ONs for page size or other constraints
derived from the page size like INLINE_EXTENT_BUFFER_PAGES.
And there's no such thing like "just bump BTRFS_MAX_COMPRESSED to 256K".
The constant is part of on-disk format for lzo and otherwise changing it
would impact performance so this would need proper evaluation.
next prev parent reply other threads:[~2021-06-10 16:23 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
2021-06-10 14:50 ` Christophe Leroy
2021-06-10 16:20 ` David Sterba [this message]
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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