David Rientjes <rientjes@xxxxxxxxxx> writes: > On Wed, 13 Jan 2016, Vitaly Kuznetsov wrote: > >> >> diff --git a/Documentation/memory-hotplug.txt b/Documentation/memory-hotplug.txt >> >> index ce2cfcf..ceaf40c 100644 >> >> --- a/Documentation/memory-hotplug.txt >> >> +++ b/Documentation/memory-hotplug.txt >> >> @@ -254,12 +254,23 @@ If the memory block is online, you'll read "online". >> >> If the memory block is offline, you'll read "offline". >> >> >> >> >> >> -5.2. How to online memory >> >> +5.2. Memory onlining >> > >> > Idk why you're changing this title since you didn't change it in the table >> > of contents and it already pairs with "6.2. How to offline memory". >> > >> > This makes it seem like you're covering all memory onlining operations in >> > the kernel (including xen onlining) rather than just memory onlined by >> > root. It doesn't cover the fact that xen onlining can be done without >> > automatic onlining, so I would leave this section's title as it is and >> > only cover aspects of memory onlining that users are triggering >> > themselves. >> >> Ok, I changed the title to reflect the fact that a special action to >> online memory is not always required any more but as the global policy >> stays 'offline' by default for now let's keep the original title. >> > > Thanks. > >> >> + /* online pages if requested */ >> >> + if (online) >> >> + online_pages(start >> PAGE_SHIFT, size >> PAGE_SHIFT, >> >> + MMOP_ONLINE_KEEP); >> >> + >> >> goto out; >> >> >> >> error: >> > >> > Well, shucks, what happens if online_pages() fails, such as if a memory >> > hot-add notifier returns an errno for MEMORY_GOING_ONLINE? The memory was >> > added but not subsequently onlined, although auto onlining was set, so how >> > does userspace know the state it is in? >> >> Bad ... we could have checked the return value but I don't see a proper >> way to handling it here: if we managed to online some blocks we can't >> revert back. We'll probably have to online pages block-by-block (e.g. by >> utilizing memory_block_change_state()) handling possible failures. >> > > My suggestion is to just simply document that auto-onlining can add the > memory but fail to online it and the failure is silent to userspace. If > userspace cares, it can check the online status of the added memory blocks > itself. The problem is not only that it's silent, but also that /sys/devices/system/memory/*/state will lie as we create all memory blocks in MEM_ONLINE state and from online_pages() error we can't figure out which particular block failed. 'v5' which I sent yesterday is supposed to fix the issue (blocks are onlined with memory_block_change_state() which handles failures. -- Vitaly -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>