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Wed, 8 Apr 2026 09:40:50 +0000 (GMT) Message-ID: Date: Wed, 8 Apr 2026 15:10:49 +0530 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] crash: Support high memory reservation for range syntax To: Youling Tang , Andrew Morton , Baoquan He , Jonathan Corbet Cc: Vivek Goyal , Dave Young , kexec@lists.infradead.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Youling Tang References: <20260404074103.506793-1-youling.tang@linux.dev> <01e47f44-c22b-42f3-afe1-4a39d9c1fd18@linux.dev> Content-Language: en-US From: Sourabh Jain In-Reply-To: <01e47f44-c22b-42f3-afe1-4a39d9c1fd18@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNDA4MDA4NCBTYWx0ZWRfXxT6V9Yqn2wqd C5VKsIN2EQvIZAP7bVSQ1VMbTNJxRrujwjoIR/cRF/zgfAq7LIRdLwYM97zd22v2tZ5ywsJy+ka VMpzreyuT6216CwSk+5pMCWtJ0GPxtNhwzvOTFK43YW23WLu7r0/dscfQHEI84d+Sfoqh5sNSyf 9ad++z08yq8yX3MI2QCtKIKcd4Zb82HFUqNVvK5Aw+/odyiLQKBUKyAo2yF5JnHXJUeVEOaXuTx heG8iqWLSX9QwmBfCEM6h3B75+h68TqLsEghWWKyOq1YnOxhM/H0wjiOGwUn+/Ic1ePk//EWFOu ju5SP8tDZFN2vPXCcg4pd3wLlbW911jXVHUjVQo1wJS81/P0RzPTgeEhp2ElNm02fhh4koTT7A2 eLG3KsVkNV9Hnv20IRqD9vU5Ml31PnWDNiBO8FlWrXEvGm1/QKZ2dqJro7111+yQaVxgr3ggxKP X6MaZxthOKQ1m0GZRUA== X-Proofpoint-ORIG-GUID: 5A2vCfFAnvmBdy9PoQCVmbL3RvEfqORJ X-Authority-Analysis: v=2.4 cv=e9k2j6p/ c=1 sm=1 tr=0 ts=69d622a7 cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=IkcTkHD0fZMA:10 a=A5OVakUREuEA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=5lQC5WIk0UPCy102QXMA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: 5A2vCfFAnvmBdy9PoQCVmbL3RvEfqORJ X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-04-08_03,2026-04-08_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 impostorscore=0 malwarescore=0 suspectscore=0 spamscore=0 bulkscore=0 adultscore=0 priorityscore=1501 phishscore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604010000 definitions=main-2604080084 On 08/04/26 13:11, Youling Tang wrote: > Hi, Sourabh > > On 4/8/26 12:31, Sourabh Jain wrote: >> Hello Youling, >> >> On 04/04/26 13:11, Youling Tang wrote: >>> From: Youling Tang >>> >>> The crashkernel range syntax (range1:size1[,range2:size2,...]) allows >>> automatic size selection based on system RAM, but it always reserves >>> from low memory. When a large crashkernel is selected, this can >>> consume most of the low memory, causing subsequent hardware >>> hotplug or drivers requiring low memory to fail due to allocation >>> failures. >> >> >> Support for high crashkernel reservation has been added to >> address the above problem. >> >> However, high crashkernel reservation is not supported with >> range-based crashkernel kernel command-line arguments. >> For example: crashkernel=0M-1G:100M,1G-4G:160M,4G-8G:192M >> >> Many users, including some distributions, use range-based >> crashkernel configuration. So, adding support for high crashkernel >> reservation with range-based configuration would be useful. >> >>> >>> Add a new optional conditional suffix ",>boundary" to the crashkernel >>> range syntax. When the selected crashkernel size exceeds the specified >>> boundary, the kernel will automatically apply the same reservation >>> policy as "crashkernel=size,high" - preferring high memory first >>> and reserving the default low memory area. >> >> I think the approach to enable high crashkernel reservation >> with range-based configuration makes the crashkernel kernel >> argument more complex. >> >> If the goal is to support high crashkernel reservation with >> range-based kernel command-line arguments, how about: >> >> crashkernel=:[,:,...][@offset],high >> >> instead of using >boundary? > > This approach defaults all reservations to high memory. For example, > 0M-2G:100M on a 1GB machine reserves 100M + > DEFAULT_CRASH_KERNEL_LOW_SIZE, > which wastes memory on small systems. OK, in that case, we need an option like >boundary because DEFAULT_CRASH_KERNEL_LOW_SIZE itself is 128 MB by default (unless the architecture overrides it). - Sourabh Jain > > I prefer small reservations defaulting to low memory, while large > reservations start from high memory (with a default-sized segment > reserved in low memory). This provides better flexibility for > distributions to handle diverse system configurations. > > Thanks, > Youling. >> >>> >>> Syntax: >>> crashkernel=:[,:,...][@offset],>boundary >>> >>> Example: >>>      crashkernel=2G-16G:512M,16G-:1G,>512M >>> >>> This means: >>>    - For 2G-16G RAM: reserve 512M normally >>>    - For >16G RAM: reserve 1G with high memory preference (since 1G >>> > 512M) >>> >>> For systems with >16G RAM, 1G is selected which exceeds 512M, so it >>> will be reserved from high memory instead of consuming 1G of >>> precious low memory. >>> >>> Signed-off-by: Youling Tang >>> --- >>>   Documentation/admin-guide/kdump/kdump.rst     | 25 ++++++++- >>>   .../admin-guide/kernel-parameters.txt         |  2 +- >>>   kernel/crash_reserve.c                        | 56 >>> ++++++++++++++++--- >>>   3 files changed, 73 insertions(+), 10 deletions(-) >>> >>> diff --git a/Documentation/admin-guide/kdump/kdump.rst >>> b/Documentation/admin-guide/kdump/kdump.rst >>> index 7587caadbae1..b5ae4556e9ca 100644 >>> --- a/Documentation/admin-guide/kdump/kdump.rst >>> +++ b/Documentation/admin-guide/kdump/kdump.rst >>> @@ -293,7 +293,28 @@ crashkernel syntax >>>          2) if the RAM size is between 512M and 2G (exclusive), then >>> reserve 64M >>>          3) if the RAM size is larger than 2G, then reserve 128M >>>   -3) crashkernel=size,high and crashkernel=size,low >>> +3) range1:size1[,range2:size2,...][@offset],>boundary >>> +   Optionally, the range list can be followed by a conditional suffix >>> +   `,>boundary`. When the selected crashkernel size matches the >>> +   condition, the kernel will reserve memory using the same policy as >>> +   `crashkernel=size,high` (i.e. prefer high memory first and >>> reserve the >>> +   default low memory area). >>> + >>> +   The syntax is:: >>> + >>> + crashkernel=:[,:,...][@offset],>boundary >>> +        range=start-[end] >>> + >>> +   For example:: >>> + >>> +        crashkernel=2G-16G:512M,16G-:1G,>512M >>> + >>> +   This would mean: >>> +       1) if the RAM size is between 2G and 16G (exclusive), then >>> reserve 512M. >>> +       2) if the RAM size is larger than 16G, allocation will >>> behave like >>> +          `crashkernel=1G,high`. >>> + >>> +4) crashkernel=size,high and crashkernel=size,low >>>        If memory above 4G is preferred, crashkernel=size,high can be >>> used to >>>      fulfill that. With it, physical memory is allowed to be >>> allocated from top, >>> @@ -311,7 +332,7 @@ crashkernel syntax >>>                 crashkernel=0,low >>>   -4) crashkernel=size,cma >>> +5) crashkernel=size,cma >>>         Reserve additional crash kernel memory from CMA. This >>> reservation is >>>       usable by the first system's userspace memory and kernel movable >>> diff --git a/Documentation/admin-guide/kernel-parameters.txt >>> b/Documentation/admin-guide/kernel-parameters.txt >>> index 03a550630644..b2e1892ab4d8 100644 >>> --- a/Documentation/admin-guide/kernel-parameters.txt >>> +++ b/Documentation/admin-guide/kernel-parameters.txt >>> @@ -1087,7 +1087,7 @@ Kernel parameters >>>               4G when '@offset' hasn't been specified. >>>               See Documentation/admin-guide/kdump/kdump.rst for >>> further details. >>>   -    crashkernel=range1:size1[,range2:size2,...][@offset] >>> + crashkernel=range1:size1[,range2:size2,...][@offset][,>boundary] >>>               [KNL] Same as above, but depends on the memory >>>               in the running system. The syntax of range is >>>               start-[end] where start and end are both >>> diff --git a/kernel/crash_reserve.c b/kernel/crash_reserve.c >>> index 62e60e0223cf..917738412390 100644 >>> --- a/kernel/crash_reserve.c >>> +++ b/kernel/crash_reserve.c >>> @@ -254,15 +254,47 @@ static __init char *get_last_crashkernel(char >>> *cmdline, >>>       return ck_cmdline; >>>   } >>>   +/* >>> + * This function parses command lines in the format >>> + * >>> + * crashkernel=ramsize-range:size[,...][@offset],>boundary >>> + */ >>> +static void __init parse_crashkernel_boundary(char *ck_cmdline, >>> +                    unsigned long long *boundary) >>> +{ >>> +    char *cur = ck_cmdline, *next; >>> +    char *first_gt = false; >>> + >>> +    first_gt = strchr(cur, '>'); >>> +    if (!first_gt) >>> +        return; >>> + >>> +    cur = first_gt + 1; >>> +    if (*cur == '\0' || *cur == ' ' || *cur == ',') { >>> +        pr_warn("crashkernel: '>' specified without boundary size, >>> ignoring\n"); >>> +        return; >>> +    } >>> + >>> +    *boundary = memparse(cur, &next); >>> +    if (cur == next) { >>> +        pr_warn("crashkernel: invalid boundary size after '>'\n"); >>> +        return; >>> +    } >>> +} >>> + >>>   static int __init __parse_crashkernel(char *cmdline, >>>                    unsigned long long system_ram, >>>                    unsigned long long *crash_size, >>>                    unsigned long long *crash_base, >>> -                 const char *suffix) >>> +                 const char *suffix, >>> +                 bool *high, >>> +                 unsigned long long *low_size) >>>   { >>>       char *first_colon, *first_space; >>>       char *ck_cmdline; >>>       char *name = "crashkernel="; >>> +    unsigned long long boundary = 0; >>> +    int ret; >>>         BUG_ON(!crash_size || !crash_base); >>>       *crash_size = 0; >>> @@ -283,10 +315,20 @@ static int __init __parse_crashkernel(char >>> *cmdline, >>>        */ >>>       first_colon = strchr(ck_cmdline, ':'); >>>       first_space = strchr(ck_cmdline, ' '); >>> -    if (first_colon && (!first_space || first_colon < first_space)) >>> -        return parse_crashkernel_mem(ck_cmdline, system_ram, >>> +    if (first_colon && (!first_space || first_colon < first_space)) { >>> +        ret = parse_crashkernel_mem(ck_cmdline, system_ram, >>>                   crash_size, crash_base); >>>   +        /* Handle optional ',>boundary' condition for range ':' >>> syntax only. */ >>> +        parse_crashkernel_boundary(ck_cmdline, &boundary); >>> +        if (!ret && *crash_size > boundary) { >>> +            *high = true; >>> +            *low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE; >>> +        } >>> + >>> +        return ret; >>> +    } >>> + >>>       return parse_crashkernel_simple(ck_cmdline, crash_size, >>> crash_base); >>>   } >>>   @@ -310,7 +352,7 @@ int __init parse_crashkernel(char *cmdline, >>>         /* crashkernel=X[@offset] */ >>>       ret = __parse_crashkernel(cmdline, system_ram, crash_size, >>> -                crash_base, NULL); >>> +                crash_base, NULL, high, low_size); >>>   #ifdef CONFIG_ARCH_HAS_GENERIC_CRASHKERNEL_RESERVATION >>>       /* >>>        * If non-NULL 'high' passed in and no normal crashkernel >>> @@ -318,7 +360,7 @@ int __init parse_crashkernel(char *cmdline, >>>        */ >>>       if (high && ret == -ENOENT) { >>>           ret = __parse_crashkernel(cmdline, 0, crash_size, >>> -                crash_base, suffix_tbl[SUFFIX_HIGH]); >>> +                crash_base, suffix_tbl[SUFFIX_HIGH], high, low_size); >>>           if (ret || !*crash_size) >>>               return -EINVAL; >>>   @@ -327,7 +369,7 @@ int __init parse_crashkernel(char *cmdline, >>>            * is not allowed. >>>            */ >>>           ret = __parse_crashkernel(cmdline, 0, low_size, >>> -                crash_base, suffix_tbl[SUFFIX_LOW]); >>> +                crash_base, suffix_tbl[SUFFIX_LOW], high, low_size); >>>           if (ret == -ENOENT) { >>>               *low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE; >>>               ret = 0; >>> @@ -344,7 +386,7 @@ int __init parse_crashkernel(char *cmdline, >>>        */ >>>       if (cma_size) >>>           __parse_crashkernel(cmdline, 0, cma_size, >>> -            &cma_base, suffix_tbl[SUFFIX_CMA]); >>> +            &cma_base, suffix_tbl[SUFFIX_CMA], high, low_size); >>>   #endif >>>       if (!*crash_size) >>>           ret = -EINVAL; >>