| Thank you for the feedback. I agree with you and would prefer to use bytes/kbytes. Here are the 2 concerns that led to me keeping it as pages:
1. Reduce the impact of the patch. Here is the call trace to reach the failure warning:
<… usual mmap() stuff …> mmap_region() -> security_enough_memory_mm() -> __vm_enough_memory()
Within mmap_region(), the length variable originally passed to mmap() gets right-shifted to get the page count. My first thought was to add an additional an additional argument to security_enough_memory_mm() of type unsigned long to keep that variable, but saw a handful of calls to it that would have to conform to the change. Not that I do not think this debug statement does not warrant that, I felt the less impact, the better.
2. Concerned about losing bits. When converting back to bytes I was worried about the loss of precision and printing that number back to users:
unsigned long bytes_failed = pages << (PAGE_SHIFT);
On Feb 22, 2024, at 6:18 AM, David Hildenbrand <david@xxxxxxxxxx> wrote:
On 21.02.24 17:02, Matthew Cassell wrote:Commit 44b414c8715c5dcf53288 ("mm/util.c: add warning if __vm_enough_memory
fails") adds debug information which gives the process id and executable name
should __vm_enough_memory() fail. Adding the number of pages to the failure
message would benefit application developers and system administrators in
debugging overambitious memory requests by providing a point of reference to
the amount of memory causing __vm_enough_memory() to fail.
1. Set appropriate kernel tunable to reach code path for failure
message:
# echo 2 > /proc/sys/vm/overcommit_memory
2. Test program to generate failure - requests 1 gibibyte per iteration:
#include <stdlib.h>
#include <stdio.h>
int main(int argc, char **argv) {
for(;;) {
if(malloc(1<<30) == NULL)
break;
printf("allocated 1 GiB\n");
}
return 0;
}
3. Output:
Before:
__vm_enough_memory: pid: 1218, comm: a.out, not enough
memory for the allocation
After:
__vm_enough_memory: pid: 1141, comm: a.out, pages: 262145, not
enough memory for the allocation
Signed-off-by: Matthew Cassell <mcassell411@xxxxxxxxx>
---
mm/util.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/mm/util.c b/mm/util.c
index 5a6a9802583b..c0afb56f16ea 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -976,8 +976,8 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
if (percpu_counter_read_positive(&vm_committed_as) < allowed)
return 0;
error:
- pr_warn_ratelimited("%s: pid: %d, comm: %s, not enough memory for the allocation\n",
- __func__, current->pid, current->comm);
+ pr_warn_ratelimited("%s: pid: %d, comm: %s, pages: %ld, not enough memory for the allocation\n",
+ __func__, current->pid, current->comm, pages);
vm_unacct_memory(pages);
return -ENOMEM;
I wonder if "bytes"/"kbytes" instead of pages would be more appropriate here.Often, this will fail due to mmap() [where we pass a size from user space] and also "vm.overcommit_kbytes" is not in pages.-- Cheers,David / dhildenb
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