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Date:   Wed, 16 Jun 2021 01:19:56 +0200
From:   Vasily Gorbik <gor@linux.ibm.com>
To:     Dimitri John Ledkov <dimitri.ledkov@canonical.com>
Cc:     linux-kernel@vger.kernel.org, Heiko Carstens <hca@linux.ibm.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        linux-s390@vger.kernel.org
Subject: Re: [PATCH] s390/boot: add zstd support
Message-ID: <your-ad-here.call-01623799196-ext-1245@work.hours>
References: <20210615114150.325080-1-dimitri.ledkov@canonical.com>
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On Tue, Jun 15, 2021 at 12:41:50PM +0100, Dimitri John Ledkov wrote:
> Enable ztsd support in s390/boot, to enable booting with zstd
> compressed kernel when configured with CONFIG_KERNEL_ZSTD=y.
> 
> BugLink: https://bugs.launchpad.net/bugs/1931725
> Signed-off-by: Dimitri John Ledkov <dimitri.ledkov@canonical.com>
> cc: Heiko Carstens <hca@linux.ibm.com>
> cc: Vasily Gorbik <gor@linux.ibm.com>
> cc: Christian Borntraeger <borntraeger@de.ibm.com>
> cc: linux-s390@vger.kernel.org
> ---
>  arch/s390/Kconfig                        | 1 +
>  arch/s390/boot/compressed/Makefile       | 4 ++++
>  arch/s390/boot/compressed/decompressor.c | 4 ++++
>  3 files changed, 9 insertions(+)

Reviewing your patch I noticed that we use wrong condition to
define BOOT_HEAP_SIZE. So I made a tiny fix:

diff --git a/arch/s390/boot/compressed/decompressor.c b/arch/s390/boot/compressed/decompressor.c
index 3061b11c4d27..cf2571050c68 100644
--- a/arch/s390/boot/compressed/decompressor.c
+++ b/arch/s390/boot/compressed/decompressor.c
@@ -29,5 +29,5 @@ extern unsigned char _compressed_start[];
 extern unsigned char _compressed_end[];
 
-#ifdef CONFIG_HAVE_KERNEL_BZIP2
+#ifdef CONFIG_KERNEL_BZIP2
 #define BOOT_HEAP_SIZE 0x400000
 #else

And applied your patch with the following changes:
Added to the commit message:
"""
BOOT_HEAP_SIZE is defined to 0x30000 in this case. Actual decompressor
memory usage with allyesconfig is currently 0x26150.
"""

diff --git a/arch/s390/boot/compressed/decompressor.c b/arch/s390/boot/compressed/decompressor.c
index cf2571050c68..37a4a8d33c6c 100644
--- a/arch/s390/boot/compressed/decompressor.c
+++ b/arch/s390/boot/compressed/decompressor.c
@@ -31,4 +31,6 @@ extern unsigned char _compressed_end[];
 #ifdef CONFIG_KERNEL_BZIP2
 #define BOOT_HEAP_SIZE 0x400000
+#elif CONFIG_KERNEL_ZSTD
+#define BOOT_HEAP_SIZE 0x30000
 #else
 #define BOOT_HEAP_SIZE 0x10000

I hope you are ok with that, thanks!