On Tue, Oct 10, 2017 at 02:45:45PM -0700, Andrew Morton wrote: > On Tue, 10 Oct 2017 13:43:43 +0800 Aaron Lu <aaron.lu@xxxxxxxxx> wrote: > > > On Mon, Oct 09, 2017 at 10:19:52PM -0700, Dave Hansen wrote: > > > On 10/09/2017 07:56 PM, Aaron Lu wrote: > > > > This patch adds inline to __rmqueue() and vmlinux' size doesn't have any > > > > change after this patch according to size(1). > > > > > > > > without this patch: > > > > text data bss dec hex filename > > > > 9968576 5793372 17715200 33477148 1fed21c vmlinux > > > > > > > > with this patch: > > > > text data bss dec hex filename > > > > 9968576 5793372 17715200 33477148 1fed21c vmlinux > > > > > > This is unexpected. Could you double-check this, please? > > > > mm/page_alloc.o has size changes: > > > > Without this patch: > > $ size mm/page_alloc.o > > text data bss dec hex filename > > 36695 9792 8396 54883 d663 mm/page_alloc.o > > > > With this patch: > > $ size mm/page_alloc.o > > text data bss dec hex filename > > 37511 9792 8396 55699 d993 mm/page_alloc.o > > > > But vmlinux doesn't. > > > > It's not clear to me what happened, do you want to me dig this out? > > There's weird stuff going on. > > With x86_64 gcc-4.8.4 > > Patch not applied: > > akpm3:/usr/local/google/home/akpm/k/25> nm mm/page_alloc.o|grep __rmqueue > 0000000000002a00 t __rmqueue > > Patch applied: > > akpm3:/usr/local/google/home/akpm/k/25> nm mm/page_alloc.o|grep __rmqueue > 000000000000039f t __rmqueue_fallback > 0000000000001220 t __rmqueue_smallest > > So inlining __rmqueue has caused the compiler to decide to uninline > __rmqueue_fallback and __rmqueue_smallest, which largely undoes the > effect of your patch. > > `inline' is basically advisory (or ignored) in modern gcc's. So gcc > has felt free to ignore it in __rmqueue_fallback and __rmqueue_smallest > because gcc thinks it knows best. That's why we created > __always_inline, to grab gcc by the scruff of its neck. This is a good point and I agree with Andi to use always_inline for those functions that we really want to inline. > > So... I think this patch could do with quite a bit more care, tuning > and testing with various gcc versions. I did some more testing. With x86_64 gcc-4.6.3 available from kernel.org crosstool: Patch not applied: [aaron@aaronlu linux]$ nm mm/page_alloc.o |grep __rmqueue 00000000000023f0 t __rmqueue 00000000000027c0 t __rmqueue_pcplist.isra.95 Patch applied: [aaron@aaronlu linux]$ nm mm/page_alloc.o |grep __rmqueue 0000000000002950 t __rmqueue_pcplist.isra.95 Works expected. With self built x86_64 gcc-4.8.4: Patch not applied: [aaron@aaronlu linux]$ nm mm/page_alloc.o |grep __rmqueue 0000000000001f20 t __rmqueue Patch applied: [aaron@aaronlu linux]$ nm mm/page_alloc.o |grep __rmqueue Works expected.(conflicts with your result though). I also tested gcc-4.9.4, gcc-5.3.1, gcc-6.4.0 and gcc-7.2.1, all have the same output as the above gcc-4.8.4. Then I realized CONFIG_OPTIMIZE_INLINING which I always disabled as suggested by the help message(If unsure, say N). Turnining that config on indeed caused gcc-4.8.4 to emit __rmqueue_fallback here. I think I'll just mark those functions always_inline. -- 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>
