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The following commit(s) were added to refs/heads/master by this push:
new a3f733d3879 fs/shm: Add a flag FS_SHMFS_NO_ALIGN to remove SHM
alignment
a3f733d3879 is described below
commit a3f733d38790e881cd552cf5e00c9c1d2a42feae
Author: Jukka Laitinen <[email protected]>
AuthorDate: Fri Aug 14 14:43:13 2026 +0300
fs/shm: Add a flag FS_SHMFS_NO_ALIGN to remove SHM alignment
This can be used on small systems to save RAM if the SHM object
doesn't need to be cache-aligned.
Signed-off-by: Jukka Laitinen <[email protected]>
---
fs/shm/Kconfig | 10 ++++++++++
fs/shm/shmfs_alloc.c | 8 ++++++++
2 files changed, 18 insertions(+)
diff --git a/fs/shm/Kconfig b/fs/shm/Kconfig
index 77bdbe5a320..1922738ccde 100644
--- a/fs/shm/Kconfig
+++ b/fs/shm/Kconfig
@@ -19,4 +19,14 @@ config FS_SHMFS_VFS_PATH
The path to where shared memory objects will exist in the VFS
namespace.
+config FS_SHMFS_NO_ALIGN
+ bool "Skip cache-line alignment/padding of shm objects"
+ default n
+ ---help---
+ Skip cache-line alignment of the shm object metadata header and
+ the object length. Saves RAM in FLAT builds where shm objects
+ are never used as DMA targets and no cache maintenance is
+ performed on their contents. Callers that need DMA-safe shm
+ buffers must not enable this.
+
endif # FS_SHMFS
diff --git a/fs/shm/shmfs_alloc.c b/fs/shm/shmfs_alloc.c
index 7b68b763cf6..0133f85a168 100644
--- a/fs/shm/shmfs_alloc.c
+++ b/fs/shm/shmfs_alloc.c
@@ -53,7 +53,11 @@ FAR struct shmfs_object_s *shmfs_alloc_object(size_t length)
size_t hdr_size = sizeof(struct shmfs_object_s);
size_t alloc_size = length;
+#ifdef CONFIG_FS_SHMFS_NO_ALIGN
+ size_t cachesize = 0;
+#else
size_t cachesize = up_get_dcache_linesize();
+#endif
if (cachesize > 0)
{
@@ -83,7 +87,11 @@ FAR struct shmfs_object_s *shmfs_alloc_object(size_t length)
object = fs_heap_zalloc(sizeof(struct shmfs_object_s));
if (object)
{
+#ifdef CONFIG_FS_SHMFS_NO_ALIGN
+ size_t cachesize = 0;
+#else
size_t cachesize = up_get_dcache_linesize();
+#endif
if (cachesize > 0)
{
