On Mon, Jun 03, 2024 at 10:55:10AM +0200, David Hildenbrand wrote: >On 02.06.24 02:58, Wei Yang wrote: >> On Sat, Jun 01, 2024 at 06:15:33PM +0200, David Hildenbrand wrote: >> > On 01.06.24 17:32, David Hildenbrand wrote: >> > > On 01.06.24 15:34, Wei Yang wrote: >> > > > Total memory represents pages managed by buddy system. >> > > >> > > No, that's managed pages. >> > > >> > > > After the >> > > > introduction of DEFERRED_STRUCT_PAGE_INIT, it may count the pages before >> > > > being managed. >> > > > >> > > >> > > I recall one reason that is done, so other subsystem know the total >> > > memory size even before deferred init is done. >> > > >> > > > free_low_memory_core_early() returns number of pages for all free pages, >> > > > even at this moment only early initialized pages are freed to buddy >> > > > system. This means the total memory at this moment is not correct. >> > > > >> > > > Let's increase it when pages are freed to buddy system. >> > > >> > > I'm missing the "why", and the very first sentence of this patch is wrong. >> > >> > Correction: your statement was correct :) That's why >> > adjust_managed_page_count() adjusts that as well. >> > >> > __free_pages_core() only adjusts managed page count, because it assumes >> > totalram has already been adjusted early during boot. >> > >> > The reason we have this split for now, I think, is because of subsystems that >> > call totalram_pages() during init. >> > >> > So the "why" question remains, because this change has the potential to break >> > other stuff. >> > >> >> Thanks, I didn't notice this. > >I think having your cleanup would be very nice, as I have patches in the >works that would benefit from being able to move the totalram update from >memory hotplug code to __free_pages_core(). > I got the same feeling. >We'd have to make sure that no code relies on totalram being sane/fixed >during boot for the initial memory. I think right now we might have such >code. > One concern is totalram would change when hotplug is enabled. That sounds those codes should do some re-calculation after totalram changes? >Further, we currently require only a single atomic RMW instruction to adjust >totalram during boot, moving it to __free_pages_core() would imply more >atomics: but usually only one per MAX_ORDER page, so I doubt this would make >a big difference. > I took a rough calculation on this.One MAX_ORDER page accounts for 2MB, and with defer_init only low zone's memory is initialized during boot. Per my understanding, low zone's memory is 4GB for x86. So the extra calculation is 4GB / 2MB = 2K. >-- >Cheers, > >David / dhildenb -- Wei Yang Help you, Help me
