Hi Catalin, On 2020/10/6 1:19, Catalin Marinas wrote: > On Mon, Sep 07, 2020 at 09:47:45PM +0800, Chen Zhou wrote: >> diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst >> index 2da65fef2a1c..549611abc581 100644 >> --- a/Documentation/admin-guide/kdump/kdump.rst >> +++ b/Documentation/admin-guide/kdump/kdump.rst > [...] >> @@ -316,8 +325,18 @@ Boot into System Kernel >> kernel will automatically locate the crash kernel image within the >> first 512MB of RAM if X is not given. >> >> - On arm64, use "crashkernel=Y[@X]". Note that the start address of >> - the kernel, X if explicitly specified, must be aligned to 2MiB (0x200000). >> + On arm64, use "crashkernel=X" to try low allocation in DMA zone, and >> + fall back to high allocation if it fails. And go for high allocation >> + directly if the required size is too large. >> + We can also use "crashkernel=X,high" to select a high region above >> + DMA zone, which also tries to allocate at least 256M low memory in >> + DMA zone automatically. >> + "crashkernel=Y,low" can be used to allocate specified size low memory >> + in DMA zone. >> + For non-RPi4 platforms, change DMA zone memtioned above to DMA32 zone. > I don't think we should mention non-RPi4 explicitly here. I don't even > understand what the suggestion is since the only way is to disable > ZONE_DMA in the kernel config. I'd just stick to ZONE_DMA description > here. How about like this: If the kernel config ZONE_DMA is disabled, just try low allocation in DMA32 zone and high allocation above DMA32 zone. Thanks, Chen Zhou > >> + Use "crashkernel=Y@X" if you really have to reserve memory from >> + specified start address X. Note that the start address of the kernel, >> + X if explicitly specified, must be aligned to 2MiB (0x200000). >> >> Load the Dump-capture Kernel >> ============================ >> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt >> index a1068742a6df..f7df572d8f64 100644 >> --- a/Documentation/admin-guide/kernel-parameters.txt >> +++ b/Documentation/admin-guide/kernel-parameters.txt >> @@ -727,6 +727,10 @@ >> [KNL, X86-64] Select a region under 4G first, and >> fall back to reserve region above 4G when '@offset' >> hasn't been specified. >> + [KNL, arm64] Try low allocation in DMA zone, fall back >> + to high allocation if it fails when '@offset' hasn't been >> + specified. For non-RPi4 platforms, change DMA zone to >> + DMA32 zone. > Same here, unclear what "change DMA zone to DMA32 zone" means. > >> See Documentation/admin-guide/kdump/kdump.rst for further details. >> >> crashkernel=range1:size1[,range2:size2,...][@offset] >> @@ -743,6 +747,8 @@ >> Otherwise memory region will be allocated below 4G, if >> available. >> It will be ignored if crashkernel=X is specified. >> + [KNL, arm64] range in high memory. >> + Allow kernel to allocate physical memory region from top. >> crashkernel=size[KMG],low >> [KNL, X86-64] range under 4G. When crashkernel=X,high >> is passed, kernel could allocate physical memory region >> @@ -751,13 +757,16 @@ >> requires at least 64M+32K low memory, also enough extra >> low memory is needed to make sure DMA buffers for 32-bit >> devices won't run out. Kernel would try to allocate at >> - at least 256M below 4G automatically. >> + least 256M below 4G automatically. >> This one let user to specify own low range under 4G >> for second kernel instead. >> 0: to disable low allocation. >> It will be ignored when crashkernel=X,high is not used >> or memory reserved is below 4G. >> - >> + [KNL, arm64] range in low memory. >> + This one let user to specify a low range in DMA zone for >> + crash dump kernel. For non-RPi4 platforms, change DMA zone >> + to DMA32 zone. > And again here. >
