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. Acked-by: Dave Young <dyoung@xxxxxxxxxx> Thanks Dave _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
