Messages in this thread | | | Subject | Re: [PATCH 2/2 v2] x86/e820: Use much less memory for e820/e820_saved, save up to 120k | From | Denys Vlasenko <> | Date | Sat, 17 Sep 2016 23:09:18 +0200 |
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On 09/15/2016 09:04 AM, Ingo Molnar wrote: > > * Denys Vlasenko <dvlasenk@redhat.com> wrote: > >> The maximum size of e820 map array for EFI systems is defined as >> E820_X_MAX (E820MAX + 3 * MAX_NUMNODES). >> >> In x86_64 defconfig, this ends up with E820_X_MAX = 320, e820 and e820_saved >> are 6404 bytes each. >> >> With larger configs, for example Fedora kernels, E820_X_MAX = 3200, e820 and e820_saved >> are 64004 bytes each. Most of this space is wasted. Typical machines have some 20-30 >> e820 areas at most. >> >> This patch turns e820 and e820_saved to pointers which initially point to __initdata >> tables, of the same size as before. >> >> At the very end of setup_arch(), when we are done fiddling with these maps, >> allocate smaller alloc_bootmem blocks, copy maps there, and change pointers. >> >> Run-tested. > >> +/* >> + * Initial e820 and e820_saved are largish __initdata arrays. >> + * Copy them to (usually much smaller) dynamically allocated area. >> + * This is done after all tweaks we ever do to them. >> + */ >> +__init void e820_reallocate_tables(void) >> +{ >> + struct e820map *n; >> + int size; >> + >> + size = offsetof(struct e820map, map) + sizeof(struct e820entry) * e820->nr_map; >> + n = alloc_bootmem(size); >> + memcpy(n, e820, size); >> + e820 = n; >> + >> + size = offsetof(struct e820map, map) + sizeof(struct e820entry) * e820_saved->nr_map; >> + n = alloc_bootmem(size); >> + memcpy(n, e820_saved, size); >> + e820_saved = n; >> +} > > Ok, this makes me quite nervous, could you please split this into two patches so > that any fails can be nicely bisected to?
No problem.
> First patch only does the pointerization changes with a trivial placeholder > structure (full size, static allocated), second patch does all the dangerous bits > such as changing it to __initdata, allocating and copying over bits. > > Also, could we please also add some minimal debugging facility to make sure the > memory table does not get extended after it's been reallocated?
I have another idea: run e820_reallocate_tables() later, just before we free __init and __initdata. Then e820 tables _can't_ be_ changed - all functions which do that are __init functions.
Will test this now, and send a patchset.
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