On 08/10/20 at 11:28am, chenzhou wrote: > On 2020/8/8 18:02, Dave Young wrote: > > On 08/01/20 at 09:08pm, Chen Zhou wrote: > >> Now the behavior of crashkernel=X has been changed, which tries low > >> allocation in ZONE_DMA, and fall back to high allocation if it fails. > >> > >> If requized size X is too large and leads to very little free memory > >> in ZONE_DMA after low allocation, the system may not work well. > >> So add a threshold and go for high allocation directly if the required > >> size is too large. The threshold is set as the half of low memory. > >> > >> If crash_base is outside ZONE_DMA, try to allocate at least 256M in > >> ZONE_DMA automatically. "crashkernel=Y,low" can be used to allocate > >> specified size low memory. For non-RPi4 platforms, change ZONE_DMA > >> memtioned above to ZONE_DMA32. > >> > >> So update the Documentation. > >> > >> Signed-off-by: Chen Zhou <chenzhou10@xxxxxxxxxx> > >> --- > >> Documentation/admin-guide/kdump/kdump.rst | 21 ++++++++++++++++--- > >> .../admin-guide/kernel-parameters.txt | 11 ++++++++-- > >> 2 files changed, 27 insertions(+), 5 deletions(-) > >> > >> diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst > >> index 2da65fef2a1c..4b58f97351d5 100644 > >> --- a/Documentation/admin-guide/kdump/kdump.rst > >> +++ b/Documentation/admin-guide/kdump/kdump.rst > >> @@ -299,7 +299,15 @@ Boot into System Kernel > >> "crashkernel=64M@16M" tells the system kernel to reserve 64 MB of memory > >> starting at physical address 0x01000000 (16MB) for the dump-capture kernel. > >> > >> - On x86 and x86_64, use "crashkernel=64M@16M". > >> + On x86 use "crashkernel=64M@16M". > >> + > >> + On x86_64, use "crashkernel=X" to select a region under 4G first, and > >> + fall back to reserve region above 4G. > >> + We can also use "crashkernel=X,high" to select a region above 4G, which > >> + also tries to allocate at least 256M below 4G automatically and > >> + "crashkernel=Y,low" can be used to allocate specified size low memory. > >> + Use "crashkernel=Y@X" if you really have to reserve memory from specified > >> + start address X. > >> > >> On ppc64, use "crashkernel=128M@32M". > >> > >> @@ -316,8 +324,15 @@ 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 ZONE_DMA, and > >> + fall back to high allocation if it fails. And go for high allocation > >> + directly if the required size is too large. If crash_base is outside > >> + ZONE_DMA, try to allocate at least 256M in ZONE_DMA automatically. > >> + "crashkernel=Y,low" can be used to allocate specified size low memory. > >> + For non-RPi4 platforms, change ZONE_DMA memtioned above to ZONE_DMA32. > >> + 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 fb95fad81c79..d1b6016850d6 100644 > >> --- a/Documentation/admin-guide/kernel-parameters.txt > >> +++ b/Documentation/admin-guide/kernel-parameters.txt > >> @@ -722,6 +722,10 @@ > >> [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 ZONE_DMA, fall back > >> + to high allocation if it fails when '@offset' hasn't been > >> + specified. For non-RPi4 platforms, change ZONE_DMA to > >> + ZONE_DMA32. > >> See Documentation/admin-guide/kdump/kdump.rst for further details. > >> > >> crashkernel=range1:size1[,range2:size2,...][@offset] > >> @@ -746,13 +750,16 @@ > >> 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 under 4G. > >> + This one let user to specify a low range in ZONE_DMA for > >> + crash dump kernel. For non-RPi4 platforms, change ZONE_DMA > >> + to ZONE_DMA32. > >> cryptomgr.notests > >> [KNL] Disable crypto self-tests > >> > >> -- > >> 2.20.1 > >> > > Hi Chen, > > > > Previously I remember we talked about to use similar logic as X86, but I > > remember you mentioned on some arm64 platform there could be no low > > memory at all. Is this not a problem now for the fallback? Just be > > curious, thanks for the update, for the common part looks good. > Hi Dave, > > Did you mean this discuss: https://lkml.org/lkml/2019/12/27/122? > This is about the different implementation instead of no low memory in arm64. > > On arm64 platform, if there is no low memory, system will boot fail. James mentioned some systems have no memory below 4G, if I understand it correctly that means they can boot without low mem. Anyway I like the new implementation in this series if it is good enough for arm64 people. > > Thanks, > Chen Zhou > > > > Acked-by: Dave Young <dyoung@xxxxxxxxxx> > > > > Thanks > > Dave > > > > > > . > > > Thanks Dave _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
