linux-kernel - Re: [resend][PATCH 4/4] oom: don't ignore rss in nascent mm

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Date:	Tue, 23 Nov 2010 15:34:27 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, pageexec@...email.hu,
	Solar Designer <solar@...nwall.com>,
	Eugene Teo <eteo@...hat.com>,
	Brad Spengler <spender@...ecurity.net>,
	Roland McGrath <roland@...hat.com>
Subject: Re: [resend][PATCH 4/4] oom: don't ignore rss in nascent mm

On 10/25, KOSAKI Motohiro wrote:
>
> Because execve() makes new mm struct and setup stack and
> copy argv. It mean the task have two mm while execve() temporary.
> Unfortunately this nascent mm is not pointed any tasks, then
> OOM-killer can't detect this memory usage. therefore OOM-killer
> may kill incorrect task.
>
> Thus, this patch added signal->in_exec_mm member and track
> nascent mm usage.

Stupid question.

Can't we just account these allocations in the old -mm temporary?

IOW. Please look at the "patch" below. It is of course incomplete
and wrong (to the point inc_mm_counter() is not safe without
SPLIT_RSS_COUNTING), and copy_strings/flush_old_exec are not the
best places to play with mm-counters, just to explain what I mean.

It is very simple. copy_strings() increments MM_ANONPAGES every
time we add a new page into bprm->vma. This makes this memory
visible to select_bad_process().

When exec changes ->mm (or if it fails), we change MM_ANONPAGES
counter back.

Most probably I missed something, but what do you think?

Oleg.

--- x/include/linux/binfmts.h
+++ x/include/linux/binfmts.h
@@ -29,6 +29,7 @@ struct linux_binprm{
 	char buf[BINPRM_BUF_SIZE];
 #ifdef CONFIG_MMU
 	struct vm_area_struct *vma;
+	unsigned long mm_anonpages;
 #else
 # define MAX_ARG_PAGES	32
 	struct page *page[MAX_ARG_PAGES];
--- x/fs/exec.c
+++ x/fs/exec.c
@@ -457,6 +457,9 @@ static int copy_strings(int argc, const 
 					goto out;
 				}
 
+				bmrp->mm_anonpages--;
+				inc_mm_counter(current->mm, MM_ANONPAGES);
+
 				if (kmapped_page) {
 					flush_kernel_dcache_page(kmapped_page);
 					kunmap(kmapped_page);
@@ -1003,6 +1006,7 @@ int flush_old_exec(struct linux_binprm *
 	/*
 	 * Release all of the old mmap stuff
 	 */
+	add_mm_counter(current->mm, bprm->mm_anonpages);
 	retval = exec_mmap(bprm->mm);
 	if (retval)
 		goto out;
@@ -1426,8 +1430,10 @@ int do_execve(const char * filename,
 	return retval;
 
 out:
-	if (bprm->mm)
-		mmput (bprm->mm);
+	if (bprm->mm) {
+		add_mm_counter(current->mm, bprm->mm_anonpages);
+		mmput(bprm->mm);
+	}
 
 out_file:
 	if (bprm->file) {

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