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Wed, 8 Apr 2026 11:32:16 +0000 (GMT) Message-ID: <9905884d-9af1-476e-9355-c2df733d9c75@linux.ibm.com> Date: Wed, 8 Apr 2026 17:02:15 +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> Content-Language: en-US From: Sourabh Jain In-Reply-To: <20260404074103.506793-1-youling.tang@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNDA4MDEwNCBTYWx0ZWRfXw/s5twIwj5ku srLl0b8nEiGgrernx/eJbrS5U4u2nfJ+wV/vdVFcd9PO/d7PeKEI1qe9PvY93uCgdkhVCZtknBy v6aNhmdlcLb8OmZSanLSpo0UTdbaILS8pS9wWVimCS8sdyB2odToc2hcwRPn4XPavllR0NBbmLe aBmW40L8qCD+VADkBqhVqjAea4vaWSNpNPkv6/4h4DV/hGZm0+rqKtxdsehQ+iezJmytHwtksof +SXeWMQ1W9UrdZ/kUNeYlY53MJBURGWTJyLh4rgwyypoxbDLnPC21ljx1+bs7y2spU+706vT8lJ YczE1HFl2UnljpNkR82aiO8f/ZW5R8H1CkuyxRXEmrEPPIbCF1hYuYtje/UV3ox5pBkVNAEF0PR 7E1+WfJ+ewJaGRuqwm+m55vqz+6VTYPs4PI14UD7NT8hd3BHSJnGAKfEyWP/zUY4Y1MhFDjIWr/ 5CoR5rsXgwn0JABGV7g== X-Authority-Analysis: v=2.4 cv=FsY1OWrq c=1 sm=1 tr=0 ts=69d63cc5 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=A5OVakUREuEA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=YjEWhN3Cx0CZYGql71AA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: UBVhWKsi9V-Xe3jkId-8tgitBtDBFFuG X-Proofpoint-GUID: UBVhWKsi9V-Xe3jkId-8tgitBtDBFFuG 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 bulkscore=0 priorityscore=1501 impostorscore=0 spamscore=0 phishscore=0 lowpriorityscore=0 clxscore=1015 adultscore=0 malwarescore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604010000 definitions=main-2604080104 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. > > 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. > > 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). Since we are mentioning that this follows same policy as crashkernel=size,high in certain cases I think it is good to mention crashkernel=size,low is ignored here. > + > + 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; false to char *? We don't even need to initialize. > + > + 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; Not all architectures support high crashkernel reservation. So high and low_size can be NULL. I think we should just skip parse_crashkernel_boundary() call if high is NULL. - Sourabh Jain > + } > + > + 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;