Date:	Wed, 1 Apr 2009 13:15:40 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	linux-kernel@...r.kernel.org
Cc:	mm-commits@...r.kernel.org, alexn@....su.se,
	akpm@...ux-foundation.org, alexn@...ia.com, apw@...dowen.org,
	cl@...ux-foundation.org, haveblue@...ibm.com,
	kamezawa.hiroyu@...fujitu.com, mel@....ul.ie,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frédéric Weisbecker <fweisbec@...il.com>
Subject: Re: + page-owner-tracking.patch added to -mm tree


* akpm@...ux-foundation.org <akpm@...ux-foundation.org> wrote:

> 
> The patch titled
>      page-owner tracking
> has been added to the -mm tree.  Its filename is
>      page-owner-tracking.patch
> 
> Before you just go and hit "reply", please:
>    a) Consider who else should be cc'ed
>    b) Prefer to cc a suitable mailing list as well
>    c) Ideally: find the original patch on the mailing list and do a
>       reply-to-all to that, adding suitable additional cc's
> 
> *** Remember to use Documentation/SubmitChecklist when testing your code ***
> 
> See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
> out what to do about this
> 
> The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
> 
> ------------------------------------------------------
> Subject: page-owner tracking
> From: Alexander Nyberg <alexn@....su.se>
> 
> > On Fri, 20 Mar 2009 15:27:00 +0000 Mel Gorman <mel@....ul.ie> wrote:
> 
> Here is a rebased reversion. Appears to work as advertised based on a
> quick test with qemu and builds without CONFIG_PROC_PAGEOWNER
> 
> 
> 
> Introduces CONFIG_PROC_PAGEOWNER that keeps track of the call chain
> under which a page was allocated.  Includes a user-space helper in
> Documentation/page_owner.c to sort the enormous amount of output that this
> may give (thanks tridge).
> 
> Information available through /proc/page_owner
> 
> x86_64 introduces some stack noise in certain call chains so for exact
> output use of x86 && CONFIG_FRAME_POINTER is suggested.  Tested on x86,
> x86 && CONFIG_FRAME_POINTER, x86_64
> 
> Output looks like:
> 
> 4819 times:
> Page allocated via order 0, mask 0x50
> [0xc012b7b9] find_lock_page+25
> [0xc012b8c8] find_or_create_page+152
> [0xc0147d74] grow_dev_page+36
> [0xc0148164] __find_get_block+84
> [0xc0147ebc] __getblk_slow+124
> [0xc0148164] __find_get_block+84
> [0xc01481e7] __getblk+55
> [0xc0185d14] do_readahead+100
> 
> We use a custom stack unwinder because using __builtin_return_address([0-7])
> causes gcc to generate code that might try to unwind the stack looking for
> function return addresses and "fall off" causing early panics if the call
> chain is not deep enough.  So in that case we could have had a depth of
> around 3 functions in all traces (I experimented a bit with this).
> 
> 
> 	make page_owner handle non-contiguous page ranges
> 
> 
> I've cleaned up the __alloc_pages() part to a simple set_page_owner() call.
> 
> Signed-off-by: Alexander Nyberg <alexn@....su.se>
> Signed-off-by: Dave Hansen <haveblue@...ibm.com>
> Signed-off-by: Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitu.com>
> DESC
> Update page->order at an appropriate time when tracking PAGE_OWNER
> EDESC
> 
> PAGE_OWNER tracks free pages by setting page->order to -1.  However, it is
> set during __free_pages() which is not the only free path as
> __pagevec_free() and free_compound_page() do not go through __free_pages().
>  This leads to a situation where free pages are visible in /proc/page_owner
> which is confusing and might be interpreted as a memory leak.
> 
> This patch sets page->owner when PageBuddy is set.  It also prints a
> warning to the kernel log if a free page is found that does not appear free
> to PAGE_OWNER.  This should be considered a fix to
> page-owner-tracking-leak-detector.patch.
> 
> This only applies to -mm as PAGE_OWNER is not in mainline.
> 
> Signed-off-by: Mel Gorman <mel@....ul.ie>
> Acked-by: Andy Whitcroft <apw@...dowen.org>
> DESC
> Print out PAGE_OWNER statistics in relation to fragmentation avoidance
> EDESC
> 
> When PAGE_OWNER is set, more information is available of relevance to
> fragmentation avoidance.  A second line is added to /proc/page_owner showing
> the PFN, the pageblock number, the mobility type of the page based on its
> allocation flags, whether the allocation is improperly placed and the flags.
> A sample entry looks like
> 
> Page allocated via order 0, mask 0x1280d2
> PFN 7355 Block 7 type 3 Fallback Flags      LA
> [0xc01528c6] __handle_mm_fault+598
> [0xc0320427] do_page_fault+279
> [0xc031ed9a] error_code+114
> 
> This information can be used to identify pages that are improperly placed.
> As the format of PAGE_OWNER data is now different, the comment at the top
> of Documentation/page_owner.c is updated with new instructions.
> 
> As PAGE_OWNER tracks the GFP flags used to allocate the pages,
> /proc/pagetypeinfo is enhanced to contain how many mixed blocks exist.
> The additional output looks like
> 
> Number of mixed blocks    Unmovable  Reclaimable      Movable      Reserve
> Node 0, zone      DMA            0            1            2            1
> Node 0, zone   Normal            2           11           33            0
> 
> Signed-off-by: Mel Gorman <mel@....ul.ie>
> Acked-by: Andy Whitcroft <apw@...dowen.org>
> Acked-by: Christoph Lameter <cl@...ux-foundation.org>
> DESC
> Allow PAGE_OWNER to be set on any architecture
> EDESC
> 
> Currently PAGE_OWNER depends on CONFIG_X86.  This appears to be due to
> pfn_to_page() being called in an inappropriate for many memory models
> and the presense of memory holes.  This patch ensures that pfn_valid()
> and pfn_valid_within() is called at the appropriate places and the offsets
> correctly updated so that PAGE_OWNER is safe on any architecture.
> 
> In situations where CONFIG_HOLES_IN_ZONES is set (IA64 with VIRTUAL_MEM_MAP),
> there may be cases where pages allocated within a MAX_ORDER_NR_PAGES block
> of pages may not be displayed in /proc/page_owner if the hole is at the
> start of the block.  Addressing this would be quite complex, perform slowly
> and is of no clear benefit.
> 
> Once PAGE_OWNER is allowed on all architectures, the statistics for grouping
> pages by mobility that declare how many pageblocks contain mixed page types
> becomes optionally available on all arches.
> 
> This patch was tested successfully on x86, x86_64, ppc64 and IA64 machines.
> 
> Signed-off-by: Mel Gorman <mel@....ul.ie>
> Acked-by: Andy Whitcroft <apw@...dowen.org>
> DESC
> allow-page_owner-to-be-set-on-any-architecture-fix
> EDESC
> 
> Cc: Andy Whitcroft <apw@...dowen.org>
> Cc: Mel Gorman <mel@....ul.ie>
> DESC
> allow-page_owner-to-be-set-on-any-architecture-fix fix
> EDESC
> 
> Page-owner-tracking stores the a backtrace of an allocation in the
> struct page.  How the stack trace is generated depends on whether
> CONFIG_FRAME_POINTER is set or not.  If CONFIG_FRAME_POINTER is set,
> the frame pointer must be read using some inline assembler which is not
> available for all architectures.
> 
> This patch uses the frame pointer where it is available but has a fallback
> where it is not.
> 
> Signed-off-by: Mel Gorman <mel@....ul.ie>
> Cc: Andy Whitcroft <apw@...dowen.org>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> 
> 
> Rebase on top of procfs changes
> 
> Signed-off-by: Mel Gorman <mel@....ul.ie>
> 
> new file mode 100644
> index 0000000..9081bd6
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> ---
> 
>  Documentation/page_owner.c |  144 +++++++++++++++++++++++++++++++++++
>  fs/proc/Makefile           |    1 
>  include/linux/mm_types.h   |    6 +
>  lib/Kconfig.debug          |   10 ++
>  mm/page_alloc.c            |   66 ++++++++++++++++
>  mm/vmstat.c                |   93 ++++++++++++++++++++++
>  6 files changed, 320 insertions(+)
> 
> diff -puN /dev/null Documentation/page_owner.c
> --- /dev/null
> +++ a/Documentation/page_owner.c
> @@ -0,0 +1,144 @@
> +/*
> + * User-space helper to sort the output of /proc/page_owner
> + *
> + * Example use:
> + * cat /proc/page_owner > page_owner_full.txt
> + * grep -v ^PFN page_owner_full.txt > page_owner.txt
> + * ./sort page_owner.txt sorted_page_owner.txt
> +*/
> +
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <sys/types.h>
> +#include <sys/stat.h>
> +#include <fcntl.h>
> +#include <unistd.h>
> +#include <string.h>
> +
> +struct block_list {
> +	char *txt;
> +	int len;
> +	int num;
> +};
> +
> +
> +static struct block_list *list;
> +static int list_size;
> +static int max_size;
> +
> +struct block_list *block_head;
> +
> +int read_block(char *buf, FILE *fin)
> +{
> +	int ret = 0;
> +	int hit = 0;
> +	char *curr = buf;
> +
> +	for (;;) {
> +		*curr = getc(fin);
> +		if (*curr == EOF) return -1;
> +
> +		ret++;
> +		if (*curr == '\n' && hit == 1)
> +			return ret - 1;
> +		else if (*curr == '\n')
> +			hit = 1;
> +		else
> +			hit = 0;
> +		curr++;
> +	}
> +}
> +
> +static int compare_txt(const void *d1, const void *d2)
> +{
> +	struct block_list *l1 = (struct block_list *)d1;
> +	struct block_list *l2 = (struct block_list *)d2;
> +	return strcmp(l1->txt, l2->txt);
> +}
> +
> +static int compare_num(const void *d1, const void *d2)
> +{
> +	struct block_list *l1 = (struct block_list *)d1;
> +	struct block_list *l2 = (struct block_list *)d2;
> +	return l2->num - l1->num;
> +}
> +
> +static void add_list(char *buf, int len)
> +{
> +	if (list_size != 0 &&
> +	    len == list[list_size-1].len &&
> +	    memcmp(buf, list[list_size-1].txt, len) == 0) {
> +		list[list_size-1].num++;
> +		return;
> +	}
> +	if (list_size == max_size) {
> +		printf("max_size too small??\n");
> +		exit(1);
> +	}
> +	list[list_size].txt = malloc(len+1);
> +	list[list_size].len = len;
> +	list[list_size].num = 1;
> +	memcpy(list[list_size].txt, buf, len);
> +	list[list_size].txt[len] = 0;
> +	list_size++;
> +	if (list_size % 1000 == 0) {
> +		printf("loaded %d\r", list_size);
> +		fflush(stdout);
> +	}
> +}
> +
> +int main(int argc, char **argv)
> +{
> +	FILE *fin, *fout;
> +	char buf[1024];
> +	int ret, i, count;
> +	struct block_list *list2;
> +	struct stat st;
> +
> +	fin = fopen(argv[1], "r");
> +	fout = fopen(argv[2], "w");
> +	if (!fin || !fout) {
> +		printf("Usage: ./program <input> <output>\n");
> +		perror("open: ");
> +		exit(2);
> +	}
> +
> +	fstat(fileno(fin), &st);
> +	max_size = st.st_size / 100; /* hack ... */
> +
> +	list = malloc(max_size * sizeof(*list));
> +
> +	for(;;) {
> +		ret = read_block(buf, fin);
> +		if (ret < 0)
> +			break;
> +
> +		buf[ret] = '\0';
> +		add_list(buf, ret);
> +	}
> +
> +	printf("loaded %d\n", list_size);
> +
> +	printf("sorting ....\n");
> +
> +	qsort(list, list_size, sizeof(list[0]), compare_txt);
> +
> +	list2 = malloc(sizeof(*list) * list_size);
> +
> +	printf("culling\n");
> +
> +	for (i=count=0;i<list_size;i++) {
> +		if (count == 0 ||
> +		    strcmp(list2[count-1].txt, list[i].txt) != 0)
> +			list2[count++] = list[i];
> +		else
> +			list2[count-1].num += list[i].num;
> +	}
> +
> +	qsort(list2, count, sizeof(list[0]), compare_num);
> +
> +	for (i=0;i<count;i++) {
> +		fprintf(fout, "%d times:\n%s\n", list2[i].num, list2[i].txt);
> +	}
> +	return 0;
> +}
> diff -puN fs/proc/Makefile~page-owner-tracking fs/proc/Makefile
> --- a/fs/proc/Makefile~page-owner-tracking
> +++ a/fs/proc/Makefile
> @@ -24,6 +24,7 @@ proc-$(CONFIG_PROC_SYSCTL)	+= proc_sysct
>  proc-$(CONFIG_NET)		+= proc_net.o
>  proc-$(CONFIG_PROC_KCORE)	+= kcore.o
>  proc-$(CONFIG_PROC_VMCORE)	+= vmcore.o
> +proc-$(CONFIG_PROC_PAGEOWNER)	+= pageowner.o
>  proc-$(CONFIG_PROC_DEVICETREE)	+= proc_devtree.o
>  proc-$(CONFIG_PRINTK)	+= kmsg.o
>  proc-$(CONFIG_PROC_PAGE_MONITOR)	+= page.o
> diff -puN include/linux/mm_types.h~page-owner-tracking include/linux/mm_types.h
> --- a/include/linux/mm_types.h~page-owner-tracking
> +++ a/include/linux/mm_types.h
> @@ -95,6 +95,12 @@ struct page {
>  	void *virtual;			/* Kernel virtual address (NULL if
>  					   not kmapped, ie. highmem) */
>  #endif /* WANT_PAGE_VIRTUAL */
> +
> +#ifdef CONFIG_PROC_PAGEOWNER
> +	int order;
> +	unsigned int gfp_mask;
> +	unsigned long trace[8];
> +#endif
>  };
>  
>  /*
> diff -puN lib/Kconfig.debug~page-owner-tracking lib/Kconfig.debug
> --- a/lib/Kconfig.debug~page-owner-tracking
> +++ a/lib/Kconfig.debug
> @@ -66,6 +66,16 @@ config UNUSED_SYMBOLS
>  	  you really need it, and what the merge plan to the mainline kernel for
>  	  your module is.
>  
> +config PROC_PAGEOWNER
> +	bool "Track page owner"
> +	depends on DEBUG_KERNEL
> +	help
> +	  This keeps track of what call chain is the owner of a page, may
> +	  help to find bare alloc_page(s) leaks. Eats a fair amount of memory.
> +	  See Documentation/page_owner.c for user-space helper.
> +
> +	  If unsure, say N.
> +
>  config DEBUG_FS
>  	bool "Debug Filesystem"
>  	depends on SYSFS
> diff -puN mm/page_alloc.c~page-owner-tracking mm/page_alloc.c
> --- a/mm/page_alloc.c~page-owner-tracking
> +++ a/mm/page_alloc.c
> @@ -359,6 +359,9 @@ static inline void set_page_order(struct
>  {
>  	set_page_private(page, order);
>  	__SetPageBuddy(page);
> +#ifdef CONFIG_PROC_PAGEOWNER
> +		page->order = -1;
> +#endif
>  }
>  
>  static inline void rmv_page_order(struct page *page)
> @@ -1458,6 +1461,62 @@ try_next_zone:
>  	return page;
>  }
>  
> +#ifdef CONFIG_PROC_PAGEOWNER
> +static inline int valid_stack_ptr(struct thread_info *tinfo, void *p)
> +{
> +	return	p > (void *)tinfo &&
> +		p < (void *)tinfo + THREAD_SIZE - 3;
> +}
> +
> +static inline void __stack_trace(struct page *page, unsigned long *stack,
> +			unsigned long bp)
> +{
> +	int i = 0;
> +	unsigned long addr;
> +	struct thread_info *tinfo = (struct thread_info *)
> +		((unsigned long)stack & (~(THREAD_SIZE - 1)));
> +
> +	memset(page->trace, 0, sizeof(long) * 8);
> +
> +#ifdef CONFIG_FRAME_POINTER
> +	if (bp) {
> +		while (valid_stack_ptr(tinfo, (void *)bp)) {
> +			addr = *(unsigned long *)(bp + sizeof(long));
> +			page->trace[i] = addr;
> +			if (++i >= 8)
> +				break;
> +			bp = *(unsigned long *)bp;
> +		}
> +		return;
> +	}
> +#endif /* CONFIG_FRAME_POINTER */
> +	while (valid_stack_ptr(tinfo, stack)) {
> +		addr = *stack++;
> +		if (__kernel_text_address(addr)) {
> +			page->trace[i] = addr;
> +			if (++i >= 8)
> +				break;
> +		}
> +	}
> +}

Uhm, this is not acceptable and broken, we have generic stacktrace 
saving facilities for this precise purpose. It has other problems 
too.

The purpose of the patch seems genuinely useful and i support the 
concept, but the current design is limiting (we could do much 
better) and the implementation is awful. Please.

Has this patch been reviewed by or Cc:-ed to anyone versed in kernel 
instrumentation details, before it was applied to -mm? Those folks 
hang around the tracing tree usually so they are easy to find. :)

	Ingo
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