Re: [PATCH] ARM: print cma-reserved pages from show_mem

From: Gregory Fong
Date: Sun Apr 12 2015 - 21:09:22 EST

On Fri, Apr 10, 2015 at 12:24:31PM +0100, Russell King - ARM Linux wrote:
> On Fri, Apr 10, 2015 at 01:18:04PM +0800, Wang, Yalin wrote:
> > > [ 12.212102] active_anon:734 inactive_anon:1189 isolated_anon:0
> > > [ 12.212102] active_file:0 inactive_file:0 isolated_file:0
> > > [ 12.212102] unevictable:0 dirty:0 writeback:0 unstable:0
> > > [ 12.212102] free:254104 slab_reclaimable:82 slab_unreclaimable:843
>
> Here, we have 82 pages reclaimable, which is 328kB, and 843 unreclaimable
> which is 3372kB, which is a total of 925 pages.
>
> > > [ 12.212102] mapped:429 shmem:1815 pagetables:13 bounce:0
> > > [ 12.212102] free_cma:4032
> > > [ 12.243172] DMA free:754080kB min:3472kB low:4340kB high:5208kB
> > > active_anon:180kB inactive_anon:0kB active_file:0kB inactive_file:0kB
> > > unevictable:0kB isolated(anon):0kB isolated(file):0kB present:778240kB
> > > managed:759252kB mlocked:0kB dirty:0kB writeback:0kB mapped:0kB
> > > shmem:0kB slab_reclaimable:328kB slab_unreclaimable:3372kB
>
> Which agrees here.
>
> > > [ 12.401609] 834 slab pages
>
> but not here... this is an interesting difference, because in the ARM
> version of show_mem(), we count the actual number of pages where
> PageSlab() returns true. Can slab pages also be reserved pages or
> swap cache pages? I thought they were exclusive of those. So, the
> question comes... why the difference in accounting, and which one is
> correct.
>
> Maybe there's a bug in the accounting somewhere...

Yes, the ARM show_mem wasn't updated after the various allocators
(SLUB, SLAB, SLOB) were updated to use compound pages. Fixing it, you
get

[ 7.081826] sysrq: SysRq : Show Memory
[ 7.085610] Mem-info:
[ 7.087890] DMA per-cpu:
[ 7.090431] CPU 0: hi: 186, btch: 31 usd: 98
[ 7.095230] HighMem per-cpu:
[ 7.098116] CPU 0: hi: 90, btch: 15 usd: 29
[ 7.102923] active_anon:724 inactive_anon:1189 isolated_anon:0
[ 7.102923] active_file:0 inactive_file:0 isolated_file:0
[ 7.102923] unevictable:0 dirty:0 writeback:0 unstable:0
[ 7.102923] free:253980 slab_reclaimable:83 slab_unreclaimable:846
[ 7.102923] mapped:429 shmem:1815 pagetables:15 bounce:0
[ 7.102923] free_cma:4032
[ 7.133995] DMA free:753344kB min:3472kB low:4340kB high:5208kB active_anon:292kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:778240kB managed:759188kB mlocked:0kB dirty:0kB writeback:0kB mapped:0kB shmem:0kB slab_reclaimable:332kB slab_unreclaimable:3384kB kernel_stack:256kB pagetables:36kB unstable:0kB bounce:0kB free_cma:0kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? yes
[ 7.174080] lowmem_reserve[]: 0 0 264 264
[ 7.178175] HighMem free:262576kB min:264kB low:572kB high:884kB active_anon:2604kB inactive_anon:4756kB active_file:0kB inactive_file:0kB unevictable:0kB isolated(anon):0kB isolated(file):0kB present:270336kB managed:270336kB mlocked:0kB dirty:0kB writeback:0kB mapped:1716kB shmem:7260kB slab_reclaimable:0kB slab_unreclaimable:0kB kernel_stack:0kB pagetables:24kB unstable:0kB bounce:0kB free_cma:16128kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? yes
[ 7.218955] lowmem_reserve[]: 0 0 0 0
[ 7.222687] DMA: 8*4kB (UEM) 8*8kB (UM) 4*16kB (UEM) 5*32kB (UM) 2*64kB (M) 4*128kB (UEM) 3*256kB (M) 2*512kB (EM) 5*1024kB (UEM) 6*2048kB (UEM) 3*4096kB (EM) 88*8192kB (MR) = 753344kB
[ 7.239477] HighMem: 0*4kB 0*8kB 1*16kB (M) 1*32kB (M) 2*64kB (UM) 2*128kB (UM) 2*256kB (UC) 3*512kB (UMC) 2*1024kB (UC) 2*2048kB (UC) 2*4096kB (UC) 30*8192kB (MRC) = 262576kB
[ 7.255455] 1815 total pagecache pages
[ 7.259211] 0 pages in swap cache
[ 7.262533] Swap cache stats: add 0, delete 0, find 0/0
[ 7.267764] Free swap = 0kB
[ 7.270647] Total swap = 0kB
[ 7.282890] 262144 pages of RAM
[ 7.286041] 254274 free pages
[ 7.289013] 4763 reserved pages
[ 7.292157] 929 slab pages
[ 7.294868] 1063 pages shared
[ 7.297839] 0 pages swap cached

And now we see 83 slab_reclaimable + 846 slab_unreclaimable adds up
correctly to the total of 929.

The patch below will end up with the correct count.

8<===
diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index 1609b02..8d606bb 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -117,7 +117,7 @@ void show_mem(unsigned int filter)
else if (PageSwapCache(page))
cached++;
else if (PageSlab(page))
- slab++;
+ slab += 1 << compound_order(page);
else if (!page_count(page))
free++;
else

--
Gregory V. Fong >< GPG key: 0BAE9648

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