Adding ZERO_PAGE detection

On some architectures ZERO_PAGE is unavailable because it references
a GPL exported symbol of empty_zero_page. Originally e08b993 removed
the call to PAGE_ZERO(0) for assignment to the abd_zero_page. However,
a simple check can be done to avoid a kernel allocation and free for
the abd_zero_page if ZERO_PAGE is available.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Brian Atkinson <batkinson@lanl.gov>
Closes #13199

diff --git a/config/kernel-zero_page.m4 b/config/kernel-zero_page.m4
new file mode 100644 (file)
index 0000000..1461781
--- /dev/null
+++ b/config/kernel-zero_page.m4
@@ -0,0 +1,27 @@
+dnl #
+dnl # ZERO_PAGE() is an alias for emtpy_zero_page. On certain architectures
+dnl # this is a GPL exported variable.
+dnl #
+
+dnl #
+dnl # Checking if ZERO_PAGE is exported GPL-only
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_SRC_ZERO_PAGE], [
+       ZFS_LINUX_TEST_SRC([zero_page], [
+               #include <asm/pgtable.h>
+       ], [
+               struct page *p __attribute__ ((unused));
+               p = ZERO_PAGE(0);
+       ], [], [ZFS_META_LICENSE])
+])
+
+AC_DEFUN([ZFS_AC_KERNEL_ZERO_PAGE], [
+       AC_MSG_CHECKING([whether ZERO_PAGE() is GPL-only])
+       ZFS_LINUX_TEST_RESULT([zero_page_license], [
+               AC_MSG_RESULT(no)
+       ], [
+               AC_MSG_RESULT(yes)
+               AC_DEFINE(HAVE_ZERO_PAGE_GPL_ONLY, 1,
+                   [ZERO_PAGE() is GPL-only])
+       ])
+])

diff --git a/config/kernel.m4 b/config/kernel.m4
index 3122e9dbaa94c4714fc1485c2a4e494d4c577be5..d1d3dede175b2c0873d675e95c8b2f3ad28ca18e 100644 (file)
--- a/config/kernel.m4
+++ b/config/kernel.m4
@@ -137,6 +137,7 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_SRC], [
        ZFS_AC_KERNEL_SRC_PAGEMAP_FOLIO_WAIT_BIT
        ZFS_AC_KERNEL_SRC_ADD_DISK
        ZFS_AC_KERNEL_SRC_KTHREAD
+       ZFS_AC_KERNEL_SRC_ZERO_PAGE
 
        AC_MSG_CHECKING([for available kernel interfaces])
        ZFS_LINUX_TEST_COMPILE_ALL([kabi])
@@ -247,6 +248,7 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_RESULT], [
        ZFS_AC_KERNEL_PAGEMAP_FOLIO_WAIT_BIT
        ZFS_AC_KERNEL_ADD_DISK
        ZFS_AC_KERNEL_KTHREAD
+       ZFS_AC_KERNEL_ZERO_PAGE
 ])
 
 dnl #

diff --git a/module/os/linux/zfs/abd_os.c b/module/os/linux/zfs/abd_os.c
index 113aee58599fc28af7ab9762138e8ae850a38718..688458621b93110184be0fdc34614c2f60e73e2b 100644 (file)
--- a/module/os/linux/zfs/abd_os.c
+++ b/module/os/linux/zfs/abd_os.c
@@ -182,8 +182,11 @@ abd_t *abd_zero_scatter = NULL;
 
 struct page;
 /*
- * abd_zero_page we will be an allocated zero'd PAGESIZE buffer, which is
- * assigned to set each of the pages of abd_zero_scatter.
+ * _KERNEL   - Will point to ZERO_PAGE if it is available or it will be
+ *             an allocated zero'd PAGESIZE buffer.
+ * Userspace - Will be an allocated zero'ed PAGESIZE buffer.
+ *
+ * abd_zero_page is assigned to each of the pages of abd_zero_scatter.
  */
 static struct page *abd_zero_page = NULL;
 
@@ -466,15 +469,19 @@ abd_alloc_zero_scatter(void)
        struct scatterlist *sg = NULL;
        struct sg_table table;
        gfp_t gfp = __GFP_NOWARN | GFP_NOIO;
-       gfp_t gfp_zero_page = gfp | __GFP_ZERO;
        int nr_pages = abd_chunkcnt_for_bytes(SPA_MAXBLOCKSIZE);
        int i = 0;
 
+#if defined(HAVE_ZERO_PAGE_GPL_ONLY)
+       gfp_t gfp_zero_page = gfp | __GFP_ZERO;
        while ((abd_zero_page = __page_cache_alloc(gfp_zero_page)) == NULL) {
                ABDSTAT_BUMP(abdstat_scatter_page_alloc_retry);
                schedule_timeout_interruptible(1);
        }
        abd_mark_zfs_page(abd_zero_page);
+#else
+       abd_zero_page = ZERO_PAGE(0);
+#endif /* HAVE_ZERO_PAGE_GPL_ONLY */
 
        while (sg_alloc_table(&table, nr_pages, gfp)) {
                ABDSTAT_BUMP(abdstat_scatter_sg_table_retry);
@@ -695,8 +702,10 @@ abd_free_zero_scatter(void)
        abd_zero_scatter = NULL;
        ASSERT3P(abd_zero_page, !=, NULL);
 #if defined(_KERNEL)
+#if defined(HAVE_ZERO_PAGE_GPL_ONLY)
        abd_unmark_zfs_page(abd_zero_page);
        __free_page(abd_zero_page);
+#endif /* HAVE_ZERO_PAGE_GPL_ONLY */
 #else
        umem_free(abd_zero_page, PAGESIZE);
 #endif /* _KERNEL */