On 07/16/2018 08:06 AM, Michal Hocko wrote: > On Sat 14-07-18 09:39:29, Pavel Tatashin wrote: > [...] >> From 95259841ef79cc17c734a994affa3714479753e3 Mon Sep 17 00:00:00 2001 >> From: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> >> Date: Sat, 14 Jul 2018 09:15:07 -0400 >> Subject: [PATCH] mm: zero unavailable pages before memmap init >> >> We must zero struct pages for memory that is not backed by physical memory, >> or kernel does not have access to. >> >> Recently, there was a change which zeroed all memmap for all holes in e820. >> Unfortunately, it introduced a bug that is discussed here: >> >> https://www.spinics.net/lists/linux-mm/msg156764.html >> >> Linus, also saw this bug on his machine, and confirmed that pulling >> commit 124049decbb1 ("x86/e820: put !E820_TYPE_RAM regions into memblock.reserved") >> fixes the issue. >> >> The problem is that we incorrectly zero some struct pages after they were >> setup. > > I am sorry but I simply do not see it. zero_resv_unavail should be > touching only reserved memory ranges and those are not initialized > anywhere. So who has reused them and put them to normal available > memory to be initialized by free_area_init_node[s]? > > The patch itself should be safe because reserved and available memory > ranges should be disjoint so the ordering shouldn't matter. The fact > that it matters is the crux thing to understand and document. So the > change looks good to me but I do not understand _why_ it makes any > difference. There must be somebody to put (memblock) reserved memory > available to the page allocator behind our backs. Thats exactly right, and I am also not sure why this is happening, there must be some overlapping happening that just should not. I will study it later. Now, I need to figure out what is happening with x86-32 failure, that is caused by my fix. Pavel
