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. > */ 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. * Skip putting upcoming bh into bh_lru until migration is done. */ if (lru_cache_disabled()) -- 2.31.0.rc2.261.g7f71774620-goog
