From 0cf14bf4b50e6be28198a517f1698f34da02a405 Mon Sep 17 00:00:00 2001 From: Rob Norris Date: Tue, 24 Sep 2024 17:17:00 +1000 Subject: [PATCH] Linux 6.12: PG_error flag was removed torvalds/linux@09022bc196d2 removes the flag, and the corresponding SetPageError() and ClearPageError() macros, with no replacement offered. Going back through the upstream history, use of this flag has been gradually removed over the last year as part of the long tail of converting everything to folios. Interesting tidbit comments from torvalds/linux@29e9412b250e and torvalds/linux@420e05d0de18 suggest that this flag has not been used meaningfully since page writeback failures started being recorded in errseq_t instead (the whole "fsyncgate" thing, ~2017, around torvalds/linux@8ed1e46aaf1b). Given that, it's possible that since perhaps Linux 4.13 we haven't been getting anything by setting the flag. I don't know if that's true and/or if there's something we should be doing instead, but my gut feel is that its probably fine we only use the page cache as a proxy to allow mmap() to work, rather than backing IO with it. As such, I'm expecting that removing this will do no harm, but I'm leaving it in for older kernels to maintain status quo, and if there is an overall better way, that is left for a future change. Sponsored-by: https://despairlabs.com/sponsor/ Reviewed-by: Brian Behlendorf Signed-off-by: Rob Norris Closes #16582 --- config/kernel-mm-page-flags.m4 | 24 +++++++++++++++++++++++ config/kernel.m4 | 2 ++ include/os/linux/kernel/linux/mm_compat.h | 14 +++++++++++++ module/os/linux/zfs/zfs_znode_os.c | 1 + 4 files changed, 41 insertions(+) create mode 100644 config/kernel-mm-page-flags.m4 diff --git a/config/kernel-mm-page-flags.m4 b/config/kernel-mm-page-flags.m4 new file mode 100644 index 000000000..b12771183 --- /dev/null +++ b/config/kernel-mm-page-flags.m4 @@ -0,0 +1,24 @@ +AC_DEFUN([ZFS_AC_KERNEL_SRC_MM_PAGE_FLAG_ERROR], [ + ZFS_LINUX_TEST_SRC([mm_page_flag_error], [ + #include + + static enum pageflags + test_flag __attribute__((unused)) = PG_error; + ]) +]) +AC_DEFUN([ZFS_AC_KERNEL_MM_PAGE_FLAG_ERROR], [ + AC_MSG_CHECKING([whether PG_error flag is available]) + ZFS_LINUX_TEST_RESULT([mm_page_flag_error], [ + AC_MSG_RESULT(yes) + AC_DEFINE(HAVE_MM_PAGE_FLAG_ERROR, 1, [PG_error flag is available]) + ],[ + AC_MSG_RESULT(no) + ]) +]) + +AC_DEFUN([ZFS_AC_KERNEL_SRC_MM_PAGE_FLAGS], [ + ZFS_AC_KERNEL_SRC_MM_PAGE_FLAG_ERROR +]) +AC_DEFUN([ZFS_AC_KERNEL_MM_PAGE_FLAGS], [ + ZFS_AC_KERNEL_MM_PAGE_FLAG_ERROR +]) diff --git a/config/kernel.m4 b/config/kernel.m4 index bfd8404cd..556df5808 100644 --- a/config/kernel.m4 +++ b/config/kernel.m4 @@ -125,6 +125,7 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_SRC], [ ZFS_AC_KERNEL_SRC_PROC_HANDLER_CTL_TABLE_CONST ZFS_AC_KERNEL_SRC_COPY_SPLICE_READ ZFS_AC_KERNEL_SRC_SYNC_BDEV + ZFS_AC_KERNEL_SRC_MM_PAGE_FLAGS ZFS_AC_KERNEL_SRC_MM_PAGE_SIZE ZFS_AC_KERNEL_SRC_MM_PAGE_MAPPING ZFS_AC_KERNEL_SRC_FILE @@ -236,6 +237,7 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_RESULT], [ ZFS_AC_KERNEL_PROC_HANDLER_CTL_TABLE_CONST ZFS_AC_KERNEL_COPY_SPLICE_READ ZFS_AC_KERNEL_SYNC_BDEV + ZFS_AC_KERNEL_MM_PAGE_FLAGS ZFS_AC_KERNEL_MM_PAGE_SIZE ZFS_AC_KERNEL_MM_PAGE_MAPPING ZFS_AC_KERNEL_1ARG_ASSIGN_STR diff --git a/include/os/linux/kernel/linux/mm_compat.h b/include/os/linux/kernel/linux/mm_compat.h index 817f6df42..4cdc0e099 100644 --- a/include/os/linux/kernel/linux/mm_compat.h +++ b/include/os/linux/kernel/linux/mm_compat.h @@ -40,4 +40,18 @@ #define page_mapping(p) folio_mapping(page_folio(p)) #endif +/* + * 6.12 removed PG_error, SetPageError and ClearPageError, with no direct + * replacement, because page writeback errors are recorded elsewhere. Since we + * only use the page cache to assist with mmap(), never directly backing it + * with IO, it shouldn't be possible for this condition to occur on our pages + * anyway, even if this is the right way to report it. So it should be safe + * to remove, but for avoidance of doubt, we make it a no-op on 6.12 and leave + * it for everything else. + */ +#ifndef HAVE_MM_PAGE_FLAG_ERROR +#define SetPageError(p) do {} while (0) +#define ClearPageError(p) do {} while (0) +#endif + #endif /* _ZFS_MM_COMPAT_H */ diff --git a/module/os/linux/zfs/zfs_znode_os.c b/module/os/linux/zfs/zfs_znode_os.c index cea15ad4b..bc1e17f08 100644 --- a/module/os/linux/zfs/zfs_znode_os.c +++ b/module/os/linux/zfs/zfs_znode_os.c @@ -58,6 +58,7 @@ #include #include #include +#include #include "zfs_prop.h" #include "zfs_comutil.h"