* Denys Vlasenko <dvlas...@redhat.com> wrote: > On 09/15/2016 09:04 AM, Ingo Molnar wrote: > > > >* Denys Vlasenko <dvlas...@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.
Could we also mark it __ro_after_init? Thanks, Ingo