Re: [PATCH v3 3/3] mm: fs: Invalidate BH LRU during page migration
From: David Hildenbrand
Date: Wed Mar 17 2021 - 07:19:19 EST
On 16.03.21 19:26, Minchan Kim wrote:
On Fri, Mar 12, 2021 at 09:17:23AM -0800, Minchan Kim wrote:
On Fri, Mar 12, 2021 at 10:33:48AM +0100, David Hildenbrand wrote:
On 12.03.21 10:03, David Hildenbrand wrote:
On 10.03.21 17:14, Minchan Kim wrote:
ffer_head LRU caches will be pinned and thus cannot be migrated.
This can prevent CMA allocations from succeeding, which are often used
on platforms with co-processors (such as a DSP) that can only use
physically contiguous memory. It can also prevent memory
hot-unplugging from succeeding, which involves migrating at least
MIN_MEMORY_BLOCK_SIZE bytes of memory, which ranges from 8 MiB to 1
GiB based on the architecture in use.
Actually, it's memory_block_size_bytes(), which can be even bigger
(IIRC, 128MiB..2 GiB on x86-64) that fails to get offlined. But that
will prevent bigger granularity (e.g., a whole DIMM) from getting unplugged.
Correspondingly, invalidate the BH LRU caches before a migration
starts and stop any buffer_head from being cached in the LRU caches,
until migration has finished.
Sounds sane to me.
Diving a bit into the code, I am wondering:
a) Are these buffer head pages marked as movable?
IOW, are they either PageLRU() or __PageMovable()?
b) How do these pages end up on ZONE_MOVABLE or MIGRATE_CMA?
I assume these pages come via
alloc_page_buffers()->alloc_buffer_head()->kmem_cache_zalloc(GFP_NOFS |
__GFP_ACCOUNT)
It's indirect it was not clear
try_to_release_page
try_to_free_buffers
buffer_busy
failed
Yeah, comment is misleading. This one would be better.
/*
* the refcount of buffer_head in bh_lru prevents dropping the
* attached page(i.e., try_to_free_buffers) so it could cause
* failing page migrationn.
* Skip putting upcoming bh into bh_lru until migration is done.
*/
Thanks, that makes more sense to me now :)
Hi Andrew,
Could you fold this comment fix patch? If you prefer formal patch,
let me know. I will resend it.
Thank you.
From 0774f21e2dc8220fc2be80c25f711cb061363519 Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@xxxxxxxxxx>
Date: Fri, 12 Mar 2021 09:17:34 -0800
Subject: [PATCH] comment fix
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
fs/buffer.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/fs/buffer.c b/fs/buffer.c
index ca9dd736bcb8..8602dcbe0327 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1265,8 +1265,9 @@ static void bh_lru_install(struct buffer_head *bh)
check_irqs_on();
/*
- * buffer_head in bh_lru could increase refcount of the page
- * until it will be invalidated. It causes page migraion failure.
+ * the refcount of buffer_head in bh_lru prevents dropping the
+ * attached page(i.e., try_to_free_buffers) so it could cause
+ * failing page migratoin.
s/migratoin/migration/
* Skip putting upcoming bh into bh_lru until migration is done.
*/
if (lru_cache_disabled())
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
--
Thanks,
David / dhildenb