On 8 Mar 2025, at 13:32, Zi Yan wrote:
> On 8 Mar 2025, at 13:14, SeongJae Park wrote:
>
>> Hello,
>>
>> On Wed, 26 Feb 2025 16:08:53 -0500 Zi Yan <ziy@xxxxxxxxxx> wrote:
>>
>>> During __filemap_add_folio(), a shadow entry is covering n slots and a
>>> folio covers m slots with m < n is to be added. Instead of splitting all
>>> n slots, only the m slots covered by the folio need to be split and the
>>> remaining n-m shadow entries can be retained with orders ranging from m to
>>> n-1. This method only requires
>>>
>>> (n/XA_CHUNK_SHIFT) - (m/XA_CHUNK_SHIFT)
>>>
>>> new xa_nodes instead of
>>> (n % XA_CHUNK_SHIFT) * ((n/XA_CHUNK_SHIFT) - (m/XA_CHUNK_SHIFT))
>>>
>>> new xa_nodes, compared to the original xas_split_alloc() + xas_split()
>>> one. For example, to insert an order-0 folio when an order-9 shadow entry
>>> is present (assuming XA_CHUNK_SHIFT is 6), 1 xa_node is needed instead of
>>> 8.
>>>
>>> xas_try_split_min_order() is introduced to reduce the number of calls to
>>> xas_try_split() during split.
>>>
>>> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
>>> Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
>>> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
>>> Cc: Kairui Song <kasong@xxxxxxxxxxx>
>>> Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
>>> Cc: Mattew Wilcox <willy@xxxxxxxxxxxxx>
>>> Cc: David Hildenbrand <david@xxxxxxxxxx>
>>> Cc: John Hubbard <jhubbard@xxxxxxxxxx>
>>> Cc: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
>>> Cc: Kirill A. Shuemov <kirill.shutemov@xxxxxxxxxxxxxxx>
>>> Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
>>> Cc: Yang Shi <yang@xxxxxxxxxxxxxxxxxxxxxx>
>>> Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
>>> ---
>>> include/linux/xarray.h | 7 +++++++
>>> lib/xarray.c | 25 +++++++++++++++++++++++
>>> mm/filemap.c | 45 +++++++++++++++++-------------------------
>>> 3 files changed, 50 insertions(+), 27 deletions(-)
>>>
>>> diff --git a/include/linux/xarray.h b/include/linux/xarray.h
>>> index 4010195201c9..78eede109b1a 100644
>>> --- a/include/linux/xarray.h
>>> +++ b/include/linux/xarray.h
>>> @@ -1556,6 +1556,7 @@ int xas_get_order(struct xa_state *xas);
>>> void xas_split(struct xa_state *, void *entry, unsigned int order);
>>> void xas_split_alloc(struct xa_state *, void *entry, unsigned int order, gfp_t);
>>> void xas_try_split(struct xa_state *xas, void *entry, unsigned int order);
>>> +unsigned int xas_try_split_min_order(unsigned int order);
>>> #else
>>> static inline int xa_get_order(struct xarray *xa, unsigned long index)
>>> {
>>> @@ -1582,6 +1583,12 @@ static inline void xas_try_split(struct xa_state *xas, void *entry,
>>> unsigned int order)
>>> {
>>> }
>>> +
>>> +static inline unsigned int xas_try_split_min_order(unsigned int order)
>>> +{
>>> + return 0;
>>> +}
>>> +
>>> #endif
>>>
>>> /**
>>> diff --git a/lib/xarray.c b/lib/xarray.c
>>> index bc197c96d171..8067182d3e43 100644
>>> --- a/lib/xarray.c
>>> +++ b/lib/xarray.c
>>> @@ -1133,6 +1133,28 @@ void xas_split(struct xa_state *xas, void *entry, unsigned int order)
>>> }
>>> EXPORT_SYMBOL_GPL(xas_split);
>>>
>>> +/**
>>> + * xas_try_split_min_order() - Minimal split order xas_try_split() can accept
>>> + * @order: Current entry order.
>>> + *
>>> + * xas_try_split() can split a multi-index entry to smaller than @order - 1 if
>>> + * no new xa_node is needed. This function provides the minimal order
>>> + * xas_try_split() supports.
>>> + *
>>> + * Return: the minimal order xas_try_split() supports
>>> + *
>>> + * Context: Any context.
>>> + *
>>> + */
>>> +unsigned int xas_try_split_min_order(unsigned int order)
>>> +{
>>> + if (order % XA_CHUNK_SHIFT == 0)
>>> + return order == 0 ? 0 : order - 1;
>>> +
>>> + return order - (order % XA_CHUNK_SHIFT);
>>> +}
>>> +EXPORT_SYMBOL_GPL(xas_try_split_min_order);
>>> +
>>
>> I found this makes build fails when CONFIG_XARRAY_MULTI is unset, like below.
>>
>> /linux/lib/xarray.c:1251:14: error: redefinition of ‘xas_try_split_min_order’
>> 1251 | unsigned int xas_try_split_min_order(unsigned int order)
>> | ^~~~~~~~~~~~~~~~~~~~~~~
>> In file included from /linux/lib/xarray.c:13:
>> /linux/include/linux/xarray.h:1587:28: note: previous definition of ‘xas_try_split_min_order’ with type ‘unsigned int(unsigned int)’
>> 1587 | static inline unsigned int xas_try_split_min_order(unsigned int order)
>> | ^~~~~~~~~~~~~~~~~~~~~~~
>>
>> I think we should have the definition only when CONFIG_XARRAY_MULTI?
>
> I think it might be a merge issue, since my original patch[1] places
> xas_try_split_min_order() above xas_try_split(), both of which are
> in #ifdef CONFIG_XARRAY_MULTI #endif. But mm-everything-2025-03-08-00-43
> seems to move xas_try_split_min_order() below xas_try_split() and
> out of CONFIG_XARRAY_MULTI guard.
>
> [1] https://lore.kernel.org/linux-mm/20250226210854.2045816-2-ziy@xxxxxxxxxx/
In addition, the new comment for xas_try_split() is added to xas_split() comment.
See https://web.git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/tree/lib/xarray.c?h=mm-everything-2025-03-08-00-43#n1084
Something went wrong when this patch was applied.
--
Best Regards,
Yan, Zi
