+ mm-do-not-increment-pgfault-stats-when-page-fault-handler-retries.patch added to mm-unstable branch

* + mm-do-not-increment-pgfault-stats-when-page-fault-handler-retries.patch added to mm-unstable branch
@ 2023-04-14 19:53 Andrew Morton
  0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2023-04-14 19:53 UTC (permalink / raw)
  To: mm-commits, willy, vbabka, punit.agrawal, minchan, michel,
	mhocko, lstoakes, Liam.Howlett, ldufour, laurent.dufour, josef,
	jack, hannes, dave, surenb, akpm


The patch titled
     Subject: mm: do not increment pgfault stats when page fault handler retries
has been added to the -mm mm-unstable branch.  Its filename is
     mm-do-not-increment-pgfault-stats-when-page-fault-handler-retries.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-do-not-increment-pgfault-stats-when-page-fault-handler-retries.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Suren Baghdasaryan <surenb@google.com>
Subject: mm: do not increment pgfault stats when page fault handler retries
Date: Fri, 14 Apr 2023 10:54:44 -0700

If the page fault handler requests a retry, we will count the fault
multiple times.  This is a relatively harmless problem as the retry paths
are not often requested, and the only user-visible problem is that the
fault counter will be slightly higher than it should be.  Nevertheless,
userspace only took one fault, and should not see the fact that the kernel
had to retry the fault multiple times.

Link: https://lkml.kernel.org/r/20230414175444.1837474-1-surenb@google.com
Fixes: d065bd810b6d ("mm: retry page fault when blocking on disk transfer")
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Jan Kara <jack@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: kernel-team@android.com
Cc: Laurent Dufour <laurent.dufour@fr.ibm.com>
Cc: Laurent Dufour <ldufour@linux.ibm.com>
Cc: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Michel Lespinasse <michel@lespinasse.org>
Cc: Minchan Kim <minchan@google.com>
Cc: Punit Agrawal <punit.agrawal@bytedance.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memory.c |   16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

--- a/mm/memory.c~mm-do-not-increment-pgfault-stats-when-page-fault-handler-retries
+++ a/mm/memory.c
@@ -5197,17 +5197,16 @@ vm_fault_t handle_mm_fault(struct vm_are
 
 	__set_current_state(TASK_RUNNING);
 
-	count_vm_event(PGFAULT);
-	count_memcg_event_mm(vma->vm_mm, PGFAULT);
-
 	ret = sanitize_fault_flags(vma, &flags);
 	if (ret)
-		return ret;
+		goto out;
 
 	if (!arch_vma_access_permitted(vma, flags & FAULT_FLAG_WRITE,
 					    flags & FAULT_FLAG_INSTRUCTION,
-					    flags & FAULT_FLAG_REMOTE))
-		return VM_FAULT_SIGSEGV;
+					    flags & FAULT_FLAG_REMOTE)) {
+		ret = VM_FAULT_SIGSEGV;
+		goto out;
+	}
 
 	/*
 	 * Enable the memcg OOM handling for faults triggered in user
@@ -5238,6 +5237,11 @@ vm_fault_t handle_mm_fault(struct vm_are
 	}
 
 	mm_account_fault(regs, address, flags, ret);
+out:
+	if (!(ret & VM_FAULT_RETRY)) {
+		count_vm_event(PGFAULT);
+		count_memcg_event_mm(vma->vm_mm, PGFAULT);
+	}
 
 	return ret;
 }
_

Patches currently in -mm which might be from surenb@google.com are

mm-do-not-increment-pgfault-stats-when-page-fault-handler-retries.patch


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