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mm/huge_memory: move folio split common code to __folio_split()

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This is a preparation patch for folio_split().

In the upcoming patch folio_split() will share folio unmapping and
remapping code with split_huge_page_to_list_to_order(), so move the code
to a common function __folio_split() first.

Add a TODO for splitting large shmem folio in swap cache.

Link: https://lkml.kernel.org/r/20250307174001.242794-4-ziy@nvidia.com
Signed-off-by: Zi Yan <ziy@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Kirill A. Shuemov <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Yang Shi <yang@os.amperecomputing.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Kairui Song <kasong@tencent.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Zi Yan
2025-03-07 12:39:56 -05:00
committed by Andrew Morton
parent 00527733d0
commit 6384dd1d18
1 changed files with 62 additions and 50 deletions
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112
mm/huge_memory.c
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@@ -3869,57 +3869,9 @@ after_split:
return ret;
}
/*
* This function splits a large folio into smaller folios of order @new_order.
* @page can point to any page of the large folio to split. The split operation
* does not change the position of @page.
*
* Prerequisites:
*
* 1) The caller must hold a reference on the @page's owning folio, also known
* as the large folio.
*
* 2) The large folio must be locked.
*
* 3) The folio must not be pinned. Any unexpected folio references, including
* GUP pins, will result in the folio not getting split; instead, the caller
* will receive an -EAGAIN.
*
* 4) @new_order > 1, usually. Splitting to order-1 anonymous folios is not
* supported for non-file-backed folios, because folio->_deferred_list, which
* is used by partially mapped folios, is stored in subpage 2, but an order-1
* folio only has subpages 0 and 1. File-backed order-1 folios are supported,
* since they do not use _deferred_list.
*
* After splitting, the caller's folio reference will be transferred to @page,
* resulting in a raised refcount of @page after this call. The other pages may
* be freed if they are not mapped.
*
* If @list is null, tail pages will be added to LRU list, otherwise, to @list.
*
* Pages in @new_order will inherit the mapping, flags, and so on from the
* huge page.
*
* Returns 0 if the huge page was split successfully.
*
* Returns -EAGAIN if the folio has unexpected reference (e.g., GUP) or if
* the folio was concurrently removed from the page cache.
*
* Returns -EBUSY when trying to split the huge zeropage, if the folio is
* under writeback, if fs-specific folio metadata cannot currently be
* released, or if some unexpected race happened (e.g., anon VMA disappeared,
* truncation).
*
* Callers should ensure that the order respects the address space mapping
* min-order if one is set for non-anonymous folios.
*
* Returns -EINVAL when trying to split to an order that is incompatible
* with the folio. Splitting to order 0 is compatible with all folios.
*/
int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
unsigned int new_order)
static int __folio_split(struct folio *folio, unsigned int new_order,
struct page *page, struct list_head *list)
{
struct folio *folio = page_folio(page);
struct deferred_split *ds_queue = get_deferred_split_queue(folio);
/* reset xarray order to new order after split */
XA_STATE_ORDER(xas, &folio->mapping->i_pages, folio->index, new_order);
@@ -3995,6 +3947,11 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
mapping = folio->mapping;
/* Truncated ? */
/*
* TODO: add support for large shmem folio in swap cache.
* When shmem is in swap cache, mapping is NULL and
* folio_test_swapcache() is true.
*/
if (!mapping) {
ret = -EBUSY;
goto out;
@@ -4129,6 +4086,61 @@ out:
return ret;
}
/*
* This function splits a large folio into smaller folios of order @new_order.
* @page can point to any page of the large folio to split. The split operation
* does not change the position of @page.
*
* Prerequisites:
*
* 1) The caller must hold a reference on the @page's owning folio, also known
* as the large folio.
*
* 2) The large folio must be locked.
*
* 3) The folio must not be pinned. Any unexpected folio references, including
* GUP pins, will result in the folio not getting split; instead, the caller
* will receive an -EAGAIN.
*
* 4) @new_order > 1, usually. Splitting to order-1 anonymous folios is not
* supported for non-file-backed folios, because folio->_deferred_list, which
* is used by partially mapped folios, is stored in subpage 2, but an order-1
* folio only has subpages 0 and 1. File-backed order-1 folios are supported,
* since they do not use _deferred_list.
*
* After splitting, the caller's folio reference will be transferred to @page,
* resulting in a raised refcount of @page after this call. The other pages may
* be freed if they are not mapped.
*
* If @list is null, tail pages will be added to LRU list, otherwise, to @list.
*
* Pages in @new_order will inherit the mapping, flags, and so on from the
* huge page.
*
* Returns 0 if the huge page was split successfully.
*
* Returns -EAGAIN if the folio has unexpected reference (e.g., GUP) or if
* the folio was concurrently removed from the page cache.
*
* Returns -EBUSY when trying to split the huge zeropage, if the folio is
* under writeback, if fs-specific folio metadata cannot currently be
* released, or if some unexpected race happened (e.g., anon VMA disappeared,
* truncation).
*
* Callers should ensure that the order respects the address space mapping
* min-order if one is set for non-anonymous folios.
*
* Returns -EINVAL when trying to split to an order that is incompatible
* with the folio. Splitting to order 0 is compatible with all folios.
*/
int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
unsigned int new_order)
{
struct folio *folio = page_folio(page);
return __folio_split(folio, new_order, page, list);
}
int min_order_for_split(struct folio *folio)
{
if (folio_test_anon(folio))