| Message ID | 20220111113314.27173-6-kirill.shutemov@linux.intel.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Implement support for unaccepted memory | expand |
On 1/11/22 03:33, Kirill A. Shutemov wrote: > Unaccepted memory bitmap is allocated during decompression stage and > handed over to main kernel image via boot_params. The bitmap is used to > track if memory has been accepted. > > Reserve unaccepted memory bitmap has to prevent reallocating memory for > other means. I'm having a hard time parsing that changelog, especially the second paragraph. Could you give it another shot? > + /* Mark unaccepted memory bitmap reserved */ > + if (boot_params.unaccepted_memory) { > + unsigned long size; > + > + /* One bit per 2MB */ > + size = DIV_ROUND_UP(e820__end_of_ram_pfn() * PAGE_SIZE, > + PMD_SIZE * BITS_PER_BYTE); > + memblock_reserve(boot_params.unaccepted_memory, size); > + } Is it OK that the size of the bitmap is inferred from e820__end_of_ram_pfn()? Is this OK in the presence of mem= and other things that muck with the e820?
On Tue, Jan 11, 2022 at 11:10:40AM -0800, Dave Hansen wrote: > On 1/11/22 03:33, Kirill A. Shutemov wrote: > > Unaccepted memory bitmap is allocated during decompression stage and > > handed over to main kernel image via boot_params. The bitmap is used to > > track if memory has been accepted. > > > > Reserve unaccepted memory bitmap has to prevent reallocating memory for > > other means. > > I'm having a hard time parsing that changelog, especially the second > paragraph. Could you give it another shot? What about this: Unaccepted memory bitmap is allocated during decompression stage and handed over to main kernel image via boot_params. Kernel tracks what memory has been accepted in the bitmap. Reserve memory where the bitmap is placed to prevent memblock from re-allocating the memory for other needs. ? > > + /* Mark unaccepted memory bitmap reserved */ > > + if (boot_params.unaccepted_memory) { > > + unsigned long size; > > + > > + /* One bit per 2MB */ > > + size = DIV_ROUND_UP(e820__end_of_ram_pfn() * PAGE_SIZE, > > + PMD_SIZE * BITS_PER_BYTE); > > + memblock_reserve(boot_params.unaccepted_memory, size); > > + } > > Is it OK that the size of the bitmap is inferred from > e820__end_of_ram_pfn()? Is this OK in the presence of mem= and other things > that muck with the e820? Good question. I think we are fine. If kernel is not able to allocate memory from a part of physical address space we don't need the bitmap for it either.
On 1/12/22 11:43 AM, Kirill A. Shutemov wrote: > On Tue, Jan 11, 2022 at 11:10:40AM -0800, Dave Hansen wrote: >> On 1/11/22 03:33, Kirill A. Shutemov wrote: >>> Unaccepted memory bitmap is allocated during decompression stage and >>> handed over to main kernel image via boot_params. The bitmap is used to >>> track if memory has been accepted. >>> >>> Reserve unaccepted memory bitmap has to prevent reallocating memory for >>> other means. >> >> I'm having a hard time parsing that changelog, especially the second >> paragraph. Could you give it another shot? > > What about this: > > Unaccepted memory bitmap is allocated during decompression stage and > handed over to main kernel image via boot_params. > > Kernel tracks what memory has been accepted in the bitmap. > > Reserve memory where the bitmap is placed to prevent memblock from > re-allocating the memory for other needs. > > ? Ahh, I get what you're trying to say now. But, it still really lacks a coherent problem statement. How about this? == Problem == A given page of memory can only be accepted once. The kernel has a need to accept memory both in the early decompression stage and during normal runtime. == Solution == Use a bitmap to communicate the acceptance state of each page between the decompression stage and normal runtime. This eliminates the possibility of attempting to double-accept a page. == Details == Allocate the bitmap during decompression stage and hand it over to the main kernel image via boot_params. In the runtime kernel, reserve the bitmap's memory to ensure nothing overwrites it. >>> + /* Mark unaccepted memory bitmap reserved */ >>> + if (boot_params.unaccepted_memory) { >>> + unsigned long size; >>> + >>> + /* One bit per 2MB */ >>> + size = DIV_ROUND_UP(e820__end_of_ram_pfn() * PAGE_SIZE, >>> + PMD_SIZE * BITS_PER_BYTE); >>> + memblock_reserve(boot_params.unaccepted_memory, size); >>> + } >> >> Is it OK that the size of the bitmap is inferred from >> e820__end_of_ram_pfn()? Is this OK in the presence of mem= and other things >> that muck with the e820? > > Good question. I think we are fine. If kernel is not able to allocate > memory from a part of physical address space we don't need the bitmap for > it either. That's a good point. If the e820 range does a one-way shrink it's probably fine. The only problem would be if the bitmap had space for for stuff past e820__end_of_ram_pfn() *and* it later needed to be accepted. Would it be worth recording the size of the reservation and then double-checking against it in the bitmap operations?
On Wed, Jan 12, 2022 at 11:53:42AM -0800, Dave Hansen wrote: > On 1/12/22 11:43 AM, Kirill A. Shutemov wrote: > > On Tue, Jan 11, 2022 at 11:10:40AM -0800, Dave Hansen wrote: > >> On 1/11/22 03:33, Kirill A. Shutemov wrote: > >> > >>> + /* Mark unaccepted memory bitmap reserved */ > >>> + if (boot_params.unaccepted_memory) { > >>> + unsigned long size; > >>> + > >>> + /* One bit per 2MB */ > >>> + size = DIV_ROUND_UP(e820__end_of_ram_pfn() * PAGE_SIZE, > >>> + PMD_SIZE * BITS_PER_BYTE); > >>> + memblock_reserve(boot_params.unaccepted_memory, size); > >>> + } > >> > >> Is it OK that the size of the bitmap is inferred from > >> e820__end_of_ram_pfn()? Is this OK in the presence of mem= and other things > >> that muck with the e820? > > > > Good question. I think we are fine. If kernel is not able to allocate > > memory from a part of physical address space we don't need the bitmap for > > it either. > > That's a good point. If the e820 range does a one-way shrink it's > probably fine. The only problem would be if the bitmap had space for > for stuff past e820__end_of_ram_pfn() *and* it later needed to be accepted. It's unlikely, but e820 can grow because of EFI and because of memmap=. To be completely on the safe side, the unaccepted bitmap should be reserved after parse_early_param() and efi_memblock_x86_reserve_range(). Since we anyway do not have memblock allocations before e820__memblock_setup(), the simplest thing would be to put the reservation first thing in e820__memblock_setup().
diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c index bc0657f0deed..dc9048e2d421 100644 --- a/arch/x86/kernel/e820.c +++ b/arch/x86/kernel/e820.c @@ -1290,6 +1290,16 @@ void __init e820__memory_setup(void) pr_info("BIOS-provided physical RAM map:\n"); e820__print_table(who); + + /* Mark unaccepted memory bitmap reserved */ + if (boot_params.unaccepted_memory) { + unsigned long size; + + /* One bit per 2MB */ + size = DIV_ROUND_UP(e820__end_of_ram_pfn() * PAGE_SIZE, + PMD_SIZE * BITS_PER_BYTE); + memblock_reserve(boot_params.unaccepted_memory, size); + } } void __init e820__memblock_setup(void)
Unaccepted memory bitmap is allocated during decompression stage and handed over to main kernel image via boot_params. The bitmap is used to track if memory has been accepted. Reserve unaccepted memory bitmap has to prevent reallocating memory for other means. Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> --- arch/x86/kernel/e820.c | 10 ++++++++++ 1 file changed, 10 insertions(+)