[patch 3/6] mm/vmalloc: Prevent flushing dirty space over and over

From: Thomas Gleixner <tglx@linutronix.de>
To: linux-mm@kvack.org
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Christoph Hellwig <hch@lst.de>,
	Uladzislau Rezki <urezki@gmail.com>,
	Lorenzo Stoakes <lstoakes@gmail.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Baoquan He <bhe@redhat.com>
Subject: [patch 3/6] mm/vmalloc: Prevent flushing dirty space over and over
Date: Tue, 23 May 2023 16:02:13 +0200 (CEST)	[thread overview]
Message-ID: <20230523140002.690874212@linutronix.de> (raw)
In-Reply-To: 20230523135902.517032811@linutronix.de

vmap blocks which have active mappings cannot be purged. Allocations which
have been freed are accounted for in vmap_block::dirty_min/max, so that
they can be detected in _vm_unmap_aliases() as potentially stale TLBs.

If there are several invocations of _vm_unmap_aliases() then each of them
will flush the dirty range. That's pointless and just increases the
probability of full TLB flushes.

Avoid that by resetting the flush range after accounting for it. That's
safe versus other invocations of _vm_unmap_aliases() because this is all
serialized with vmap_purge_lock.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 mm/vmalloc.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2224,7 +2224,7 @@ static void vb_free(unsigned long addr,
 
 	spin_lock(&vb->lock);
 
-	/* Expand dirty range */
+	/* Expand the not yet TLB flushed dirty range */
 	vb->dirty_min = min(vb->dirty_min, offset);
 	vb->dirty_max = max(vb->dirty_max, offset + (1UL << order));
 
@@ -2262,7 +2262,7 @@ static void _vm_unmap_aliases(unsigned l
 			 * space to be flushed.
 			 */
 			if (!purge_fragmented_block(vb, vbq, &purge_list) &&
-			    vb->dirty && vb->dirty != VMAP_BBMAP_BITS) {
+			    vb->dirty_max && vb->dirty != VMAP_BBMAP_BITS) {
 				unsigned long va_start = vb->va->va_start;
 				unsigned long s, e;
 
@@ -2272,6 +2272,10 @@ static void _vm_unmap_aliases(unsigned l
 				start = min(s, start);
 				end   = max(e, end);
 
+				/* Prevent that this is flushed more than once */
+				vb->dirty_min = VMAP_BBMAP_BITS;
+				vb->dirty_max = 0;
+
 				flush = 1;
 			}
 			spin_unlock(&vb->lock);


