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Message-ID: <20250213034355.516610-2-ziy@nvidia.com>
Date: Wed, 12 Feb 2025 22:43:54 -0500
From: Zi Yan <ziy@...dia.com>
To: Matthew Wilcox <willy@...radead.org>,
linux-mm@...ck.org,
linux-fsdevel@...r.kernel.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Hugh Dickins <hughd@...gle.com>,
Baolin Wang <baolin.wang@...ux.alibaba.com>,
Kairui Song <kasong@...cent.com>,
Miaohe Lin <linmiaohe@...wei.com>,
linux-kernel@...r.kernel.org,
Zi Yan <ziy@...dia.com>
Subject: [PATCH 1/2] mm/filemap: use xas_try_split() in __filemap_add_folio().
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@...dia.com>
---
include/linux/xarray.h | 7 +++++++
lib/xarray.c | 25 +++++++++++++++++++++++
mm/filemap.c | 46 +++++++++++++++++-------------------------
3 files changed, 51 insertions(+), 27 deletions(-)
diff --git a/include/linux/xarray.h b/include/linux/xarray.h
index 9eb8c7425090..6ef3d682b189 100644
--- a/include/linux/xarray.h
+++ b/include/linux/xarray.h
@@ -1557,6 +1557,7 @@ 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,
gfp_t gfp);
+unsigned int xas_try_split_min_order(unsigned int order);
#else
static inline int xa_get_order(struct xarray *xa, unsigned long index)
{
@@ -1583,6 +1584,12 @@ static inline void xas_try_split(struct xa_state *xas, void *entry,
unsigned int order, gfp_t gfp)
{
}
+
+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 c38beca77830..1805fde1c361 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);
+
/**
* xas_try_split() - Try to split a multi-index entry.
* @xas: XArray operation state.
@@ -1145,6 +1167,9 @@ EXPORT_SYMBOL_GPL(xas_split);
* be allocated, the function will use @gfp to get one. If more xa_node are
* needed, the function gives EINVAL error.
*
+ * NOTE: use xas_try_split_min_order() to get next split order instead of
+ * @order - 1 if you want to minmize xas_try_split() calls.
+ *
* Context: Any context. The caller should hold the xa_lock.
*/
void xas_try_split(struct xa_state *xas, void *entry, unsigned int order,
diff --git a/mm/filemap.c b/mm/filemap.c
index 804d7365680c..e28a7a623889 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -860,11 +860,10 @@ EXPORT_SYMBOL_GPL(replace_page_cache_folio);
noinline int __filemap_add_folio(struct address_space *mapping,
struct folio *folio, pgoff_t index, gfp_t gfp, void **shadowp)
{
- XA_STATE(xas, &mapping->i_pages, index);
- void *alloced_shadow = NULL;
- int alloced_order = 0;
+ XA_STATE_ORDER(xas, &mapping->i_pages, index, folio_order(folio));
bool huge;
long nr;
+ unsigned int forder = folio_order(folio);
VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
VM_BUG_ON_FOLIO(folio_test_swapbacked(folio), folio);
@@ -873,7 +872,6 @@ noinline int __filemap_add_folio(struct address_space *mapping,
mapping_set_update(&xas, mapping);
VM_BUG_ON_FOLIO(index & (folio_nr_pages(folio) - 1), folio);
- xas_set_order(&xas, index, folio_order(folio));
huge = folio_test_hugetlb(folio);
nr = folio_nr_pages(folio);
@@ -883,7 +881,7 @@ noinline int __filemap_add_folio(struct address_space *mapping,
folio->index = xas.xa_index;
for (;;) {
- int order = -1, split_order = 0;
+ int order = -1;
void *entry, *old = NULL;
xas_lock_irq(&xas);
@@ -901,21 +899,26 @@ noinline int __filemap_add_folio(struct address_space *mapping,
order = xas_get_order(&xas);
}
- /* entry may have changed before we re-acquire the lock */
- if (alloced_order && (old != alloced_shadow || order != alloced_order)) {
- xas_destroy(&xas);
- alloced_order = 0;
- }
-
if (old) {
- if (order > 0 && order > folio_order(folio)) {
+ if (order > 0 && order > forder) {
+ unsigned int split_order = max(forder,
+ xas_try_split_min_order(order));
+
/* How to handle large swap entries? */
BUG_ON(shmem_mapping(mapping));
- if (!alloced_order) {
- split_order = order;
- goto unlock;
+
+ while (order > forder) {
+ xas_set_order(&xas, index, split_order);
+ xas_try_split(&xas, old, order,
+ GFP_NOWAIT);
+ if (xas_error(&xas))
+ goto unlock;
+ order = split_order;
+ split_order =
+ max(xas_try_split_min_order(
+ split_order),
+ forder);
}
- xas_split(&xas, old, order);
xas_reset(&xas);
}
if (shadowp)
@@ -939,17 +942,6 @@ noinline int __filemap_add_folio(struct address_space *mapping,
unlock:
xas_unlock_irq(&xas);
- /* split needed, alloc here and retry. */
- if (split_order) {
- xas_split_alloc(&xas, old, split_order, gfp);
- if (xas_error(&xas))
- goto error;
- alloced_shadow = old;
- alloced_order = split_order;
- xas_reset(&xas);
- continue;
- }
-
if (!xas_nomem(&xas, gfp))
break;
}
--
2.47.2
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