Re: [PATCH v3 11/16] bcache: handle cache set verify_ondisk properly for bucket size > 8MB

[Hannes Reinecke <hare@suse.de>]

On 7/15/20 4:30 PM, colyli@suse.de wrote:
> From: Coly Li <colyli@suse.de>
> 
> In bch_btree_cache_alloc() when CONFIG_BCACHE_DEBUG is configured,
> allocate memory for c->verify_ondisk may fail if the bucket size > 8MB,
> which will require __get_free_pages() to allocate continuous pages
> with order > 11 (the default MAX_ORDER of Linux buddy allocator). Such
> over size allocation will fail, and cause 2 problems,
> - When CONFIG_BCACHE_DEBUG is configured,  bch_btree_verify() does not
>    work, because c->verify_ondisk is NULL and bch_btree_verify() returns
>    immediately.
> - bch_btree_cache_alloc() will fail due to c->verify_ondisk allocation
>    failed, then the whole cache device registration fails. And because of
>    this failure, the first problem of bch_btree_verify() has no chance to
>    be triggered.
> 
> This patch fixes the above problem by two means,
> 1) If pages allocation of c->verify_ondisk fails, set it to NULL and
>     returns bch_btree_cache_alloc() with -ENOMEM.
> 2) When calling __get_free_pages() to allocate c->verify_ondisk pages,
>     use ilog2(meta_bucket_pages(&c->sb)) to make sure ilog2() will always
>     generate a pages order <= MAX_ORDER (or CONFIG_FORCE_MAX_ZONEORDER).
>     Then the buddy system won't directly reject the allocation request.
> 
> Signed-off-by: Coly Li <colyli@suse.de>
> ---
>   drivers/md/bcache/btree.c | 12 ++++++++++--
>   1 file changed, 10 insertions(+), 2 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke            Teamlead Storage & Networking
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