Re: [PATCH v3] mm: release private data before split THP

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 10 Aug 2022 14:49:07 +0800 Yin Fengwei <fengwei.yin@intel.com> wrote:

> If there is private data attached to THP, the refcount of
> THP will be increased and block the THP split. Release
> private data attached to THP before split it to increase
> the chance of splitting THP successfully.
> 
> There was a memory failure issue hit during HW error
> injection testing with 5.18 kernel + xfs as rootfs. Test
> got killed and system reboot was required to re-run the
> test.
> 
> The issue was tracked down to THP split failure caused the
> memory failure not being handled. The page dump showed:
> 
> [ 1785.433075] page:0000000025f9530b refcount:18 mapcount:0 mapping:000000008162eea7 index:0xa10 pfn:0x2f0200
> [ 1785.443954] head:0000000025f9530b order:4 compound_mapcount:0 compound_pincount:0
> [ 1785.452408] memcg:ff4247f2d28e9000
> [ 1785.456304] aops:xfs_address_space_operations ino:8555182 dentry name:"baseos-filenames.solvx"
> [ 1785.466612] flags: 0x1000000000012036(referenced|uptodate|lru|active|private|head|node=0|zone=2)
> [ 1785.476514] raw: 1000000000012036 ffb9460f8bc07c08 ffb9460f8bc08408 ff4247f22e6299f8
> [ 1785.485268] raw: 0000000000000a10 ff4247f194ade900 00000012ffffffff ff4247f2d28e9000
> 
> It was like the error was injected to a large folio for xfs
> with private data attached.
> 
> With private data released before split THP, the test case
> could be run successfully many times without reboot system.

I did a bit of editorial work on the changelog.  Please check, Note my
addition of "attempt to" to the second sentence.

: If there is private data attached to a THP, the refcount of THP will be
: increased and will prevent the THP from being split.  Attempt to release
: any private data attached to the THP before attempting the split to
: increase the chance of splitting successfully.
: 
: There was a memory failure issue hit during HW error injection testing
: with 5.18 kernel + xfs as rootfs.  The test was killed and a system reboot
: was required to re-run the test.
: 
: The issue was tracked down to a THP split failure caused by the memory
: failure not being handled.  The page dump showed:
: 
: [ 1785.433075] page:0000000025f9530b refcount:18 mapcount:0 mapping:000000008162eea7 index:0xa10 pfn:0x2f0200
: [ 1785.443954] head:0000000025f9530b order:4 compound_mapcount:0 compound_pincount:0
: [ 1785.452408] memcg:ff4247f2d28e9000
: [ 1785.456304] aops:xfs_address_space_operations ino:8555182 dentry name:"baseos-filenames.solvx"
: [ 1785.466612] flags: 0x1000000000012036(referenced|uptodate|lru|active|private|head|node=0|zone=2)
: [ 1785.476514] raw: 1000000000012036 ffb9460f8bc07c08 ffb9460f8bc08408 ff4247f22e6299f8
: [ 1785.485268] raw: 0000000000000a10 ff4247f194ade900 00000012ffffffff ff4247f2d28e9000
: 
: It was like the error was injected to a large folio for xfs with private
: data attached.
: 
: With private data released before splitting the THP, the test case could
: be run successfully many times without rebooting the system.

> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
>
> ...
>
> @@ -2635,8 +2637,16 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
>  			goto out;
>  		}
>  
> -		xas_split_alloc(&xas, head, compound_order(head),
> -				mapping_gfp_mask(mapping) & GFP_RECLAIM_MASK);
> +		gfp = current_gfp_context(mapping_gfp_mask(mapping) &
> +							GFP_RECLAIM_MASK);
> +
> +		if (folio_test_private(folio) &&
> +				!filemap_release_folio(folio, gfp)) {
> +			ret = -EBUSY;
> +			goto out;
> +		}
> +
> +		xas_split_alloc(&xas, head, compound_order(head), gfp);

Because I assume we run into the same problem if
filemap_release_folio() fails?