On 12.11.24 08:45, Baolin Wang wrote:
Add large folio support for tmpfs write and fallocate paths matching the
same high order preference mechanism used in the iomap buffered IO path
as used in __filemap_get_folio().
Add shmem_mapping_size_orders() to get a hint for the orders of the folio
based on the file size which takes care of the mapping requirements.
Traditionally, tmpfs only supported PMD-sized huge folios. However nowadays
with other file systems supporting any sized large folios, and extending
anonymous to support mTHP, we should not restrict tmpfs to allocating only
PMD-sized huge folios, making it more special. Instead, we should allow
tmpfs can allocate any sized large folios.
Considering that tmpfs already has the 'huge=' option to control the huge
folios allocation, we can extend the 'huge=' option to allow any sized huge
folios. The semantics of the 'huge=' mount option are:
huge=never: no any sized huge folios
huge=always: any sized huge folios
huge=within_size: like 'always' but respect the i_size
huge=advise: like 'always' if requested with fadvise()/madvise()
Note: for tmpfs mmap() faults, due to the lack of a write size hint, still
allocate the PMD-sized huge folios if huge=always/within_size/advise is set.
Moreover, the 'deny' and 'force' testing options controlled by
'/sys/kernel/mm/transparent_hugepage/shmem_enabled', still retain the same
semantics. The 'deny' can disable any sized large folios for tmpfs, while
the 'force' can enable PMD sized large folios for tmpfs.
Co-developed-by: Daniel Gomez <da.gomez@xxxxxxxxxxx>
Signed-off-by: Daniel Gomez <da.gomez@xxxxxxxxxxx>
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
mm/shmem.c | 91 +++++++++++++++++++++++++++++++++++++++++++++---------
1 file changed, 77 insertions(+), 14 deletions(-)
diff --git a/mm/shmem.c b/mm/shmem.c
index 86b2e417dc6f..a3203cf8860f 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -549,10 +549,50 @@ static bool shmem_confirm_swap(struct address_space *mapping,
static int shmem_huge __read_mostly = SHMEM_HUGE_NEVER;
+/**
+ * shmem_mapping_size_orders - Get allowable folio orders for the given file size.
+ * @mapping: Target address_space.
+ * @index: The page index.
+ * @write_end: end of a write, could extend inode size.
+ *
+ * This returns huge orders for folios (when supported) based on the file size
+ * which the mapping currently allows at the given index. The index is relevant
+ * due to alignment considerations the mapping might have. The returned order
+ * may be less than the size passed.
+ *
+ * Return: The orders.
+ */
+static inline unsigned int
+shmem_mapping_size_orders(struct address_space *mapping, pgoff_t index, loff_t write_end)
+{
+ unsigned int order;
+ size_t size;
+
+ if (!mapping_large_folio_support(mapping) || !write_end)
+ return 0;
+
+ /* Calculate the write size based on the write_end */
+ size = write_end - (index << PAGE_SHIFT);
+ order = filemap_get_order(size);
+ if (!order)
+ return 0;
+
+ /* If we're not aligned, allocate a smaller folio */
+ if (index & ((1UL << order) - 1))
+ order = __ffs(index);
+
+ order = min_t(size_t, order, MAX_PAGECACHE_ORDER);
+ return order > 0 ? BIT(order + 1) - 1 : 0;
+}
+
static unsigned int shmem_huge_global_enabled(struct inode *inode, pgoff_t index,
loff_t write_end, bool shmem_huge_force,
+ struct vm_area_struct *vma,
unsigned long vm_flags)
{
+ unsigned long within_size_orders;
+ unsigned int order;
+ pgoff_t aligned_index;
loff_t i_size;
if (HPAGE_PMD_ORDER > MAX_PAGECACHE_ORDER)
We can allow all orders up to MAX_PAGECACHE_ORDER,
shmem_mapping_size_orders() handles it properly.
So maybe we should drop this condition and use instead below where we have
return BIT(HPAGE_PMD_ORDER);
instead something like.
return HPAGE_PMD_ORDER > MAX_PAGECACHE_ORDER ? 0 : BIT(HPAGE_PMD_ORDER);
Ideally, factoring it out somehow
int maybe_pmd_order = HPAGE_PMD_ORDER > MAX_PAGECACHE_ORDER ? 0 :
BIT(HPAGE_PMD_ORDER);
...
return maybe_pmd_order;
@@ -564,15 +604,41 @@ static unsigned int shmem_huge_global_enabled(struct inode *inode, pgoff_t index
if (shmem_huge_force || shmem_huge == SHMEM_HUGE_FORCE)
return BIT(HPAGE_PMD_ORDER);
Why not force-enable all orders (of course, respecting
MAX_PAGECACHE_ORDER and possibly VMA)?
+ /*
+ * The huge order allocation for anon shmem is controlled through
+ * the mTHP interface, so we still use PMD-sized huge order to
+ * check whether global control is enabled.
+ *
+ * For tmpfs mmap()'s huge order, we still use PMD-sized order to
+ * allocate huge pages due to lack of a write size hint.
+ *
+ * Otherwise, tmpfs will allow getting a highest order hint based on
+ * the size of write and fallocate paths, then will try each allowable
+ * huge orders.
+ */
switch (SHMEM_SB(inode->i_sb)->huge) {
case SHMEM_HUGE_ALWAYS:
- return BIT(HPAGE_PMD_ORDER);
- case SHMEM_HUGE_WITHIN_SIZE:
- index = round_up(index + 1, HPAGE_PMD_NR);
- i_size = max(write_end, i_size_read(inode));
- i_size = round_up(i_size, PAGE_SIZE);
- if (i_size >> PAGE_SHIFT >= index)
+ if (vma)
return BIT(HPAGE_PMD_ORDER);
+
+ return shmem_mapping_size_orders(inode->i_mapping, index, write_end);
+ case SHMEM_HUGE_WITHIN_SIZE:
+ if (vma)
+ within_size_orders = BIT(HPAGE_PMD_ORDER);
+ else
+ within_size_orders = shmem_mapping_size_orders(inode->i_mapping,
+ index, write_end);
+
+ order = highest_order(within_size_orders);
+ while (within_size_orders) {
+ aligned_index = round_up(index + 1, 1 << order);
+ i_size = max(write_end, i_size_read(inode));
+ i_size = round_up(i_size, PAGE_SIZE);
+ if (i_size >> PAGE_SHIFT >= aligned_index)
+ return within_size_orders;
+
+ order = next_order(&within_size_orders, order);
+ }
fallthrough;
case SHMEM_HUGE_ADVISE:
if (vm_flags & VM_HUGEPAGE)
I think the point here is that "write" -> no VMA -> vm_flags == 0 -> no
code changes needed :)
