Re: [PATCH] lib/alloc_tag: Remove the sysctl configuration to prevent users from disabling it at runtime
From: Hao Ge
Date: Wed Nov 13 2024 - 01:07:44 EST
On 11/12/24 23:26, Suren Baghdasaryan wrote:
On Mon, Nov 11, 2024 at 7:31 PM Hao Ge <hao.ge@xxxxxxxxx> wrote:
Hi Suren
Firstly, please forgive me for my improper wording in the commit message.
After sending it, I realized that I should have used "suggestion"
instead of "decided".
Secondly, please forgive me for taking a few days to respond. I've been
quite busy these days.
No worries.
Let's continue to discuss this issue.
On 11/9/24 02:16, Suren Baghdasaryan wrote:
On Thu, Nov 7, 2024 at 11:50 PM Hao Ge <hao.ge@xxxxxxxxx> wrote:
From: Hao Ge <gehao@xxxxxxxxxx>
After much consideration,I have decided to remove
the "mem_profiling" sysctl interface to prevent
users from dynamically enabling or disabling the
MEMORY ALLOCATION PROFILING feature at runtime.
I have taken the following actions: I set
CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT=y to
enable memory allocation profiling by default,
and then made adjustments to mem_profiling dynamically
during runtime.
When I ran the OOM test program, I obtained useful
information that was indeed very helpful for debugging.
[ 1023.065402] Memory allocations:
[ 1023.065407] 12.8 GiB 6546 mm/huge_memory.c:1328 func:do_huge_pmd_anonymous_page
[ 1023.065412] 873 MiB 229985 arch/arm64/mm/fault.c:986 func:vma_alloc_zeroed_movable_folio
[ 1023.065415] 187 MiB 29732 mm/slub.c:2412 func:alloc_slab_page
[ 1023.065418] 99.8 MiB 25560 mm/memory.c:1065 func:folio_prealloc
[ 1023.065421] 47.2 MiB 3189 mm/readahead.c:434 func:ra_alloc_folio
[ 1023.065424] 30.0 MiB 15 mm/khugepaged.c:1072 func:alloc_charge_folio
[ 1023.065428] 28.6 MiB 514 mm/compaction.c:1880 func:compaction_alloc
[ 1023.065430] 25.8 MiB 6592 mm/page_ext.c:271 func:alloc_page_ext
[ 1023.065433] 25.6 MiB 6546 mm/huge_memory.c:1161 func:__do_huge_pmd_anonymous_page
[ 1023.065436] 23.5 MiB 6017 mm/shmem.c:1771 func:shmem_alloc_folio
After running echo 0 > /proc/sys/vm/mem_profiling
and then executing the same test program,
I obtained the following results
[ 1156.509699] Memory allocations:
[ 1156.509703] 187 MiB 29645 mm/slub.c:2412 func:alloc_slab_page
[ 1156.509707] 142 MiB 9357 mm/readahead.c:434 func:ra_alloc_folio
[ 1156.509710] 136 MiB 41325 arch/arm64/mm/fault.c:986 func:vma_alloc_zeroed_movable_folio
[ 1156.509713] 99.7 MiB 25531 mm/memory.c:1065 func:folio_prealloc
[ 1156.509716] 56.0 MiB 28 mm/huge_memory.c:1328 func:do_huge_pmd_anonymous_page
[ 1156.509719] 30.0 MiB 15 mm/khugepaged.c:1072 func:alloc_charge_folio
[ 1156.509723] 28.6 MiB 514 mm/compaction.c:1880 func:compaction_alloc
[ 1156.509725] 26.3 MiB 7460 mm/readahead.c:264 func:page_cache_ra_unbounded
[ 1156.509728] 25.8 MiB 6592 mm/page_ext.c:271 func:alloc_page_ext
[ 1156.509730] 23.5 MiB 6016 mm/shmem.c:1771 func:shmem_alloc_folio
Because mem_profiling was disabled by executing
echo 0 > /proc/sys/vm/mem_profiling,we are unable to
record memory allocation information after the disablement.
Naturally you are unable to track the allocations after disabling it.
You disabled it as root, so I assume you know what you are doing.
These output logs can mislead users. And similarly, the same
applies to alloc_info.
I would understand if you made /proc/allocinfo empty after disabling
it to avoid confusing the user, but ripping out the ability to
enable/disable profiling at runtime does not make sense to me. Once
you collect required data, disabling profiling gets you back the
performance that you pay for it. There are usecases when a program on
a remote device periodically enables profiling for some time, records
the difference in allocations and then disables it. Your change breaks
such users.
Actually, my original intention was also to make /proc/allocinfo empty
when disabling it,
but I considered the following scenario: after we disable it and clear
/proc/allocinfo,
we then start a memory-intensive application,
such as our OOM (Out-Of-Memory) test program.
If we later enable it again, the issue described in my commit message
would still arise.
The absolute values won't mean anything once profiling is disabled. In
cases when profiling gets disabled, the only useful way to use it
again is to enable it and record the initial states, let your workload
run, capture the states after the workload is complete and compare it
with the recorded initial state. Deltas can be useful, the absolute
values would not matter.
But maybe I'm not getting your usecase. Could you please explain what
you are trying to achieve and what are your expectations of how
profiling should act?
Thanks,
Suren.
Hi Suren
Thank you for your patient discussion on this matter.
For me, this tool is very useful for analyzing certain memory issues.
For a server product, there may be more than one system administrator
(i.e., more than one root user).
Perhaps Administrator A turned it off, but Administrator B was unaware
of this, which led to confusion about the logs I mentioned.
After your and Kent's patient explanations, I now understand that this
switch indeed serves a purpose.
Thank you both for your answers, which have deepened my understanding.
For example, if I want to analyze the memory usage from initialization
to the present,
disabled can help me eliminate the impact of subsequent changes.
My initial idea and this patch had some flaws. Indeed, we only need to
provide the appropriate functions for users to choose from,
and it is up to them to decide how to use them.
Thank you very much for teaching me something new.
Thanks
Best regards
Hao
Perhaps we need to further consider how to handle this situation.
Thanks Best regards Hao
We already have boot parameters that allow users to
choose whether to enable or disable.
In order to maintain the accuracy of memory allocation
information,I have decided to remove the runtime switch.
Well, I disagree with your decision.
NAK.
Signed-off-by: Hao Ge <gehao@xxxxxxxxxx>
---
lib/alloc_tag.c | 26 --------------------------
1 file changed, 26 deletions(-)
diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
index 81e5f9a70f22..47fa969c23f3 100644
--- a/lib/alloc_tag.c
+++ b/lib/alloc_tag.c
@@ -227,31 +227,6 @@ struct page_ext_operations page_alloc_tagging_ops = {
};
EXPORT_SYMBOL(page_alloc_tagging_ops);
-#ifdef CONFIG_SYSCTL
-static struct ctl_table memory_allocation_profiling_sysctls[] = {
- {
- .procname = "mem_profiling",
- .data = &mem_alloc_profiling_key,
-#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG
- .mode = 0444,
-#else
- .mode = 0644,
-#endif
- .proc_handler = proc_do_static_key,
- },
-};
-
-static void __init sysctl_init(void)
-{
- if (!mem_profiling_support)
- memory_allocation_profiling_sysctls[0].mode = 0444;
-
- register_sysctl_init("vm", memory_allocation_profiling_sysctls);
-}
-#else /* CONFIG_SYSCTL */
-static inline void sysctl_init(void) {}
-#endif /* CONFIG_SYSCTL */
-
static int __init alloc_tag_init(void)
{
const struct codetag_type_desc desc = {
@@ -264,7 +239,6 @@ static int __init alloc_tag_init(void)
if (IS_ERR(alloc_tag_cttype))
return PTR_ERR(alloc_tag_cttype);
- sysctl_init();
procfs_init();
return 0;
--
2.25.1