| Message ID | 20190417054559.29252-1-amir73il@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v4] fs/sync.c: sync_file_range(2) may use WB_SYNC_ALL writeback | expand |
On Wed, Apr 17, 2019 at 08:45:59AM +0300, Amir Goldstein wrote: > Commit 23d0127096cb ("fs/sync.c: make sync_file_range(2) use WB_SYNC_NONE > writeback") claims that sync_file_range(2) syscall was "created for > userspace to be able to issue background writeout and so waiting for > in-flight IO is undesirable there" and changes the writeback (back) to > WB_SYNC_NONE. > > This claim is only partially true. It is true for users that use the flag > SYNC_FILE_RANGE_WRITE by itself, as does PostgreSQL, the user that was > the reason for changing to WB_SYNC_NONE writeback. > > However, that claim is not true for users that use that flag combination > SYNC_FILE_RANGE_{WAIT_BEFORE|WRITE|_WAIT_AFTER}. > Those users explicitly requested to wait for in-flight IO as well as to > writeback of dirty pages. > > Re-brand that flag combination as SYNC_FILE_RANGE_WRITE_AND_WAIT > and use the helper filemap_write_and_wait_range(), that uses WB_SYNC_ALL > writeback, to perform the full range sync request. > > Link: http://lkml.kernel.org/r/20190409114922.30095-1-amir73il@gmail.com > Fixes: 23d0127096cb ("fs/sync.c: make sync_file_range(2) use WB_SYNC_NONE") > Signed-off-by: Amir Goldstein <amir73il@gmail.com> > Acked-by: Jan Kara <jack@suse.com> > Cc: Dave Chinner <david@fromorbit.com> > Cc: Al Viro <viro@zeniv.linux.org.uk> > --- > > Andrew, > > V2 of this patch is on your mmtotm queue. > However, I had already sent out V3 with a braino fix and Dave Chinner > just added more review comments which I had addressed in this version. > > Thanks, > Amir. > > Changes since v3: > - Remove unneeded change to VALID_FLAGS (Dave) > - Call file_fdatawait_range() before writeback (Dave) > > Changes since v2: > - Return after filemap_write_and_wait_range() > > Changes since v1: > - Remove non-guaranties of the API from commit message > - Added ACK by Jan > > fs/sync.c | 20 +++++++++++++++----- > include/uapi/linux/fs.h | 3 +++ > 2 files changed, 18 insertions(+), 5 deletions(-) > > diff --git a/fs/sync.c b/fs/sync.c > index b54e0541ad89..1836328f1ae8 100644 > --- a/fs/sync.c > +++ b/fs/sync.c > @@ -235,9 +235,9 @@ SYSCALL_DEFINE1(fdatasync, unsigned int, fd) > } > > /* > - * sys_sync_file_range() permits finely controlled syncing over a segment of > + * ksys_sync_file_range() permits finely controlled syncing over a segment of > * a file in the range offset .. (offset+nbytes-1) inclusive. If nbytes is > - * zero then sys_sync_file_range() will operate from offset out to EOF. > + * zero then ksys_sync_file_range() will operate from offset out to EOF. > * > * The flag bits are: > * > @@ -254,7 +254,7 @@ SYSCALL_DEFINE1(fdatasync, unsigned int, fd) > * Useful combinations of the flag bits are: > * > * SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE: ensures that all pages > - * in the range which were dirty on entry to sys_sync_file_range() are placed > + * in the range which were dirty on entry to ksys_sync_file_range() are placed > * under writeout. This is a start-write-for-data-integrity operation. > * > * SYNC_FILE_RANGE_WRITE: start writeout of all dirty pages in the range which > @@ -266,10 +266,13 @@ SYSCALL_DEFINE1(fdatasync, unsigned int, fd) > * earlier SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE operation to wait > * for that operation to complete and to return the result. > * > - * SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE|SYNC_FILE_RANGE_WAIT_AFTER: > + * SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE|SYNC_FILE_RANGE_WAIT_AFTER > + * (a.k.a. SYNC_FILE_RANGE_WRITE_AND_WAIT): > * a traditional sync() operation. This is a write-for-data-integrity operation > * which will ensure that all pages in the range which were dirty on entry to > - * sys_sync_file_range() are committed to disk. > + * ksys_sync_file_range() are written to disk. It should be noted that disk > + * caches are not flushed by this call, so there are no guarantees here that the > + * data will be available on disk after a crash. > * > * > * SYNC_FILE_RANGE_WAIT_BEFORE and SYNC_FILE_RANGE_WAIT_AFTER will detect any > @@ -344,6 +347,13 @@ int ksys_sync_file_range(int fd, loff_t offset, loff_t nbytes, > goto out_put; > } > > + if ((flags & SYNC_FILE_RANGE_WRITE_AND_WAIT) == > + SYNC_FILE_RANGE_WRITE_AND_WAIT) { > + /* Unlike SYNC_FILE_RANGE_WRITE alone, uses WB_SYNC_ALL */ > + ret = filemap_write_and_wait_range(mapping, offset, endbyte); > + goto out_put; > + } Clunky, now that I look at it in context. + int sync_mode = WB_SYNC_NONE; + + if ((flags & SYNC_FILE_RANGE_WRITE_AND_WAIT) == + SYNC_FILE_RANGE_WRITE_AND_WAIT) + sync_mode = WB_SYNC_ALL; ..... if (flags & SYNC_FILE_RANGE_WRITE) { ret = __filemap_fdatawrite_range(mapping, offset, endbyte, - WB_SYNC_NONE); + sync_mode); Cheers, Dave.
diff --git a/fs/sync.c b/fs/sync.c index b54e0541ad89..1836328f1ae8 100644 --- a/fs/sync.c +++ b/fs/sync.c @@ -235,9 +235,9 @@ SYSCALL_DEFINE1(fdatasync, unsigned int, fd) } /* - * sys_sync_file_range() permits finely controlled syncing over a segment of + * ksys_sync_file_range() permits finely controlled syncing over a segment of * a file in the range offset .. (offset+nbytes-1) inclusive. If nbytes is - * zero then sys_sync_file_range() will operate from offset out to EOF. + * zero then ksys_sync_file_range() will operate from offset out to EOF. * * The flag bits are: * @@ -254,7 +254,7 @@ SYSCALL_DEFINE1(fdatasync, unsigned int, fd) * Useful combinations of the flag bits are: * * SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE: ensures that all pages - * in the range which were dirty on entry to sys_sync_file_range() are placed + * in the range which were dirty on entry to ksys_sync_file_range() are placed * under writeout. This is a start-write-for-data-integrity operation. * * SYNC_FILE_RANGE_WRITE: start writeout of all dirty pages in the range which @@ -266,10 +266,13 @@ SYSCALL_DEFINE1(fdatasync, unsigned int, fd) * earlier SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE operation to wait * for that operation to complete and to return the result. * - * SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE|SYNC_FILE_RANGE_WAIT_AFTER: + * SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE|SYNC_FILE_RANGE_WAIT_AFTER + * (a.k.a. SYNC_FILE_RANGE_WRITE_AND_WAIT): * a traditional sync() operation. This is a write-for-data-integrity operation * which will ensure that all pages in the range which were dirty on entry to - * sys_sync_file_range() are committed to disk. + * ksys_sync_file_range() are written to disk. It should be noted that disk + * caches are not flushed by this call, so there are no guarantees here that the + * data will be available on disk after a crash. * * * SYNC_FILE_RANGE_WAIT_BEFORE and SYNC_FILE_RANGE_WAIT_AFTER will detect any @@ -344,6 +347,13 @@ int ksys_sync_file_range(int fd, loff_t offset, loff_t nbytes, goto out_put; } + if ((flags & SYNC_FILE_RANGE_WRITE_AND_WAIT) == + SYNC_FILE_RANGE_WRITE_AND_WAIT) { + /* Unlike SYNC_FILE_RANGE_WRITE alone, uses WB_SYNC_ALL */ + ret = filemap_write_and_wait_range(mapping, offset, endbyte); + goto out_put; + } + if (flags & SYNC_FILE_RANGE_WRITE) { ret = __filemap_fdatawrite_range(mapping, offset, endbyte, WB_SYNC_NONE); diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h index 121e82ce296b..59c71fa8c553 100644 --- a/include/uapi/linux/fs.h +++ b/include/uapi/linux/fs.h @@ -320,6 +320,9 @@ struct fscrypt_key { #define SYNC_FILE_RANGE_WAIT_BEFORE 1 #define SYNC_FILE_RANGE_WRITE 2 #define SYNC_FILE_RANGE_WAIT_AFTER 4 +#define SYNC_FILE_RANGE_WRITE_AND_WAIT (SYNC_FILE_RANGE_WRITE | \ + SYNC_FILE_RANGE_WAIT_BEFORE | \ + SYNC_FILE_RANGE_WAIT_AFTER) /* * Flags for preadv2/pwritev2:
Commit 23d0127096cb ("fs/sync.c: make sync_file_range(2) use WB_SYNC_NONE writeback") claims that sync_file_range(2) syscall was "created for userspace to be able to issue background writeout and so waiting for in-flight IO is undesirable there" and changes the writeback (back) to WB_SYNC_NONE. This claim is only partially true. It is true for users that use the flag SYNC_FILE_RANGE_WRITE by itself, as does PostgreSQL, the user that was the reason for changing to WB_SYNC_NONE writeback. However, that claim is not true for users that use that flag combination SYNC_FILE_RANGE_{WAIT_BEFORE|WRITE|_WAIT_AFTER}. Those users explicitly requested to wait for in-flight IO as well as to writeback of dirty pages. Re-brand that flag combination as SYNC_FILE_RANGE_WRITE_AND_WAIT and use the helper filemap_write_and_wait_range(), that uses WB_SYNC_ALL writeback, to perform the full range sync request. Link: http://lkml.kernel.org/r/20190409114922.30095-1-amir73il@gmail.com Fixes: 23d0127096cb ("fs/sync.c: make sync_file_range(2) use WB_SYNC_NONE") Signed-off-by: Amir Goldstein <amir73il@gmail.com> Acked-by: Jan Kara <jack@suse.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Al Viro <viro@zeniv.linux.org.uk> --- Andrew, V2 of this patch is on your mmtotm queue. However, I had already sent out V3 with a braino fix and Dave Chinner just added more review comments which I had addressed in this version. Thanks, Amir. Changes since v3: - Remove unneeded change to VALID_FLAGS (Dave) - Call file_fdatawait_range() before writeback (Dave) Changes since v2: - Return after filemap_write_and_wait_range() Changes since v1: - Remove non-guaranties of the API from commit message - Added ACK by Jan fs/sync.c | 20 +++++++++++++++----- include/uapi/linux/fs.h | 3 +++ 2 files changed, 18 insertions(+), 5 deletions(-)