* [Devel] [PATCH vz10] fs: move FALLOC_FL_PREALLOCATE to a bit upstream has not taken
@ 2026-09-08 13:38 Konstantin Khorenko
2026-09-08 13:43 ` Alexey Kuznetsov
2026-09-08 14:25 ` Konstantin Khorenko
0 siblings, 2 replies; 3+ messages in thread
From: Konstantin Khorenko @ 2026-09-08 13:38 UTC (permalink / raw)
To: Alexey Kuznetsov; +Cc: Denis V. Lunev, devel
We had FALLOC_FL_PREALLOCATE == 0x80.
Upstream commit 7bd43cc79cab ("fs: introduce FALLOC_FL_WRITE_ZEROES to
fallocate"), released in v6.17, gives 0x80 to a mode of its own and
adds it to FALLOC_FL_MODE_MASK.
Move the mode to 0x00100000, well above the range upstream allocates
modes from and away from the top of the word, where a future user is
just as likely to start.
The number cannot simply change, though, because userspace carries its
own copy of it. Export the value as a read-only ext4 module parameter,
/sys/module/ext4/parameters/falloc_fl_preallocate, and let userspace
read the mode from there.
The old value stays accepted as FALLOC_FL_PREALLOCATE_OLD, so that
userspace built before this change keeps working. It has to be dropped
before the rebase onto v6.17 or later, otherwise we would take
FALLOC_FL_WRITE_ZEROES requests for our own mode.
Feature: ext4: preallocation flag for small fallocates
https://virtuozzo.atlassian.net/browse/VSTOR-144521
Signed-off-by: Konstantin Khorenko <khorenko@virtuozzo.com>
---
Follow-up to the v3 thread of "fs/ext4: let FALLOC_FL_PREALLOCATE
through the vfs_fallocate mode switch": 0x80 is FALLOC_FL_WRITE_ZEROES
upstream since v6.17, so our mode has to move before we rebase onto it,
and the value has to become discoverable instead of hardcoded on both
sides.
---
fs/ext4/extents.c | 14 ++++++++++----
fs/open.c | 1 +
include/linux/falloc.h | 3 ++-
include/uapi/linux/falloc.h | 15 ++++++++++++++-
4 files changed, 27 insertions(+), 6 deletions(-)
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 38f50770f6585..eca3f0312ac53 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -39,6 +39,10 @@ static unsigned int falloc_prealloc;
module_param(falloc_prealloc, uint, 0644);
MODULE_PARM_DESC(falloc_prealloc, "Preallocate fallocate like it is a write for smaller sizes");
+static unsigned int falloc_fl_preallocate = FALLOC_FL_PREALLOCATE;
+module_param(falloc_fl_preallocate, uint, 0444);
+MODULE_PARM_DESC(falloc_fl_preallocate, "fallocate() mode value asking for preallocation");
+
/*
* used by extent splitting.
*/
@@ -4514,8 +4518,8 @@ static int ext4_alloc_file_blocks(struct file *file, ext4_lblk_t offset,
* that it doesn't get unnecessarily split into multiple
* extents.
*/
- if (!(mode & FALLOC_FL_PREALLOCATE) && len <= EXT_UNWRITTEN_MAX_LEN &&
- len > falloc_prealloc)
+ if (!(mode & (FALLOC_FL_PREALLOCATE | FALLOC_FL_PREALLOCATE_OLD)) &&
+ len <= EXT_UNWRITTEN_MAX_LEN && len > falloc_prealloc)
flags |= EXT4_GET_BLOCKS_NO_NORMALIZE;
/*
@@ -4754,7 +4758,8 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
/* Return error if mode is not supported */
if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |
FALLOC_FL_COLLAPSE_RANGE | FALLOC_FL_ZERO_RANGE |
- FALLOC_FL_INSERT_RANGE | FALLOC_FL_PREALLOCATE))
+ FALLOC_FL_INSERT_RANGE | FALLOC_FL_PREALLOCATE |
+ FALLOC_FL_PREALLOCATE_OLD))
return -EOPNOTSUPP;
inode_lock(inode);
@@ -4770,7 +4775,8 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
goto out_inode_lock;
if ((mode & FALLOC_FL_MODE_MASK) == FALLOC_FL_ALLOCATE_RANGE ||
- (mode & FALLOC_FL_MODE_MASK) == FALLOC_FL_PREALLOCATE) {
+ (mode & FALLOC_FL_MODE_MASK) == FALLOC_FL_PREALLOCATE ||
+ (mode & FALLOC_FL_MODE_MASK) == FALLOC_FL_PREALLOCATE_OLD) {
ret = ext4_do_fallocate(file, offset, len, mode);
goto out_inode_lock;
}
diff --git a/fs/open.c b/fs/open.c
index fc72ad09e7e81..65c96bf03dc93 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -268,6 +268,7 @@ int vfs_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
case FALLOC_FL_UNSHARE_RANGE:
case FALLOC_FL_ZERO_RANGE:
case FALLOC_FL_PREALLOCATE:
+ case FALLOC_FL_PREALLOCATE_OLD:
break;
case FALLOC_FL_PUNCH_HOLE:
if (!(mode & FALLOC_FL_KEEP_SIZE))
diff --git a/include/linux/falloc.h b/include/linux/falloc.h
index f6eee099b3fca..58e991ea6771f 100644
--- a/include/linux/falloc.h
+++ b/include/linux/falloc.h
@@ -37,7 +37,8 @@ struct space_resv {
FALLOC_FL_ZERO_RANGE | \
FALLOC_FL_INSERT_RANGE | \
FALLOC_FL_UNSHARE_RANGE | \
- FALLOC_FL_PREALLOCATE)
+ FALLOC_FL_PREALLOCATE | \
+ FALLOC_FL_PREALLOCATE_OLD)
/* on ia32 l_start is on a 32-bit boundary */
#if defined(CONFIG_X86_64)
diff --git a/include/uapi/linux/falloc.h b/include/uapi/linux/falloc.h
index 7ac8ffb8e6523..49aa826ad8f8a 100644
--- a/include/uapi/linux/falloc.h
+++ b/include/uapi/linux/falloc.h
@@ -78,6 +78,19 @@
*/
#define FALLOC_FL_UNSHARE_RANGE 0x40
-#define FALLOC_FL_PREALLOCATE 0x80
+/*
+ * FALLOC_FL_PREALLOCATE tells the filesystem to allocate the range the way a
+ * write would, with mballoc preallocation, rather than trimming the request
+ * down to a single unwritten extent.
+ *
+ * Userspace may read the mode value from
+ * /sys/module/ext4/parameters/falloc_fl_preallocate.
+ *
+ * FALLOC_FL_PREALLOCATE_OLD is the value used before upstream v6.17 claimed
+ * 0x80 for FALLOC_FL_WRITE_ZEROES. It is accepted as an alias of the above,
+ * and has to be dropped before a rebase onto v6.17 or later.
+ */
+#define FALLOC_FL_PREALLOCATE_OLD 0x80
+#define FALLOC_FL_PREALLOCATE 0x00100000
#endif /* _UAPI_FALLOC_H_ */
---
base-commit: 3466ec0b2cdf9d49dbb36d7b5ed9b36dfb2fb04d
change-id: 20260908-pr-khorenko-vstor-144521-falloc_fl_preallocate-cec80ce87000
Best regards,
--
Konstantin Khorenko <khorenko@virtuozzo.com>
_______________________________________________
Devel mailing list
Devel@openvz.org
https://lists.openvz.org/mailman/listinfo/devel
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Devel] [PATCH vz10] fs: move FALLOC_FL_PREALLOCATE to a bit upstream has not taken
2026-09-08 13:38 [Devel] [PATCH vz10] fs: move FALLOC_FL_PREALLOCATE to a bit upstream has not taken Konstantin Khorenko
@ 2026-09-08 13:43 ` Alexey Kuznetsov
2026-09-08 14:25 ` Konstantin Khorenko
1 sibling, 0 replies; 3+ messages in thread
From: Alexey Kuznetsov @ 2026-09-08 13:43 UTC (permalink / raw)
To: Konstantin Khorenko; +Cc: Denis V. Lunev, devel
Ack.
On Tue, Sep 8, 2026 at 9:41 PM Konstantin Khorenko
<khorenko@virtuozzo.com> wrote:
>
> We had FALLOC_FL_PREALLOCATE == 0x80.
>
> Upstream commit 7bd43cc79cab ("fs: introduce FALLOC_FL_WRITE_ZEROES to
> fallocate"), released in v6.17, gives 0x80 to a mode of its own and
> adds it to FALLOC_FL_MODE_MASK.
>
> Move the mode to 0x00100000, well above the range upstream allocates
> modes from and away from the top of the word, where a future user is
> just as likely to start.
>
> The number cannot simply change, though, because userspace carries its
> own copy of it. Export the value as a read-only ext4 module parameter,
> /sys/module/ext4/parameters/falloc_fl_preallocate, and let userspace
> read the mode from there.
>
> The old value stays accepted as FALLOC_FL_PREALLOCATE_OLD, so that
> userspace built before this change keeps working. It has to be dropped
> before the rebase onto v6.17 or later, otherwise we would take
> FALLOC_FL_WRITE_ZEROES requests for our own mode.
>
> Feature: ext4: preallocation flag for small fallocates
>
> https://virtuozzo.atlassian.net/browse/VSTOR-144521
>
> Signed-off-by: Konstantin Khorenko <khorenko@virtuozzo.com>
> ---
> Follow-up to the v3 thread of "fs/ext4: let FALLOC_FL_PREALLOCATE
> through the vfs_fallocate mode switch": 0x80 is FALLOC_FL_WRITE_ZEROES
> upstream since v6.17, so our mode has to move before we rebase onto it,
> and the value has to become discoverable instead of hardcoded on both
> sides.
> ---
> fs/ext4/extents.c | 14 ++++++++++----
> fs/open.c | 1 +
> include/linux/falloc.h | 3 ++-
> include/uapi/linux/falloc.h | 15 ++++++++++++++-
> 4 files changed, 27 insertions(+), 6 deletions(-)
>
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 38f50770f6585..eca3f0312ac53 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -39,6 +39,10 @@ static unsigned int falloc_prealloc;
> module_param(falloc_prealloc, uint, 0644);
> MODULE_PARM_DESC(falloc_prealloc, "Preallocate fallocate like it is a write for smaller sizes");
>
> +static unsigned int falloc_fl_preallocate = FALLOC_FL_PREALLOCATE;
> +module_param(falloc_fl_preallocate, uint, 0444);
> +MODULE_PARM_DESC(falloc_fl_preallocate, "fallocate() mode value asking for preallocation");
> +
> /*
> * used by extent splitting.
> */
> @@ -4514,8 +4518,8 @@ static int ext4_alloc_file_blocks(struct file *file, ext4_lblk_t offset,
> * that it doesn't get unnecessarily split into multiple
> * extents.
> */
> - if (!(mode & FALLOC_FL_PREALLOCATE) && len <= EXT_UNWRITTEN_MAX_LEN &&
> - len > falloc_prealloc)
> + if (!(mode & (FALLOC_FL_PREALLOCATE | FALLOC_FL_PREALLOCATE_OLD)) &&
> + len <= EXT_UNWRITTEN_MAX_LEN && len > falloc_prealloc)
> flags |= EXT4_GET_BLOCKS_NO_NORMALIZE;
>
> /*
> @@ -4754,7 +4758,8 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
> /* Return error if mode is not supported */
> if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |
> FALLOC_FL_COLLAPSE_RANGE | FALLOC_FL_ZERO_RANGE |
> - FALLOC_FL_INSERT_RANGE | FALLOC_FL_PREALLOCATE))
> + FALLOC_FL_INSERT_RANGE | FALLOC_FL_PREALLOCATE |
> + FALLOC_FL_PREALLOCATE_OLD))
> return -EOPNOTSUPP;
>
> inode_lock(inode);
> @@ -4770,7 +4775,8 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
> goto out_inode_lock;
>
> if ((mode & FALLOC_FL_MODE_MASK) == FALLOC_FL_ALLOCATE_RANGE ||
> - (mode & FALLOC_FL_MODE_MASK) == FALLOC_FL_PREALLOCATE) {
> + (mode & FALLOC_FL_MODE_MASK) == FALLOC_FL_PREALLOCATE ||
> + (mode & FALLOC_FL_MODE_MASK) == FALLOC_FL_PREALLOCATE_OLD) {
> ret = ext4_do_fallocate(file, offset, len, mode);
> goto out_inode_lock;
> }
> diff --git a/fs/open.c b/fs/open.c
> index fc72ad09e7e81..65c96bf03dc93 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -268,6 +268,7 @@ int vfs_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
> case FALLOC_FL_UNSHARE_RANGE:
> case FALLOC_FL_ZERO_RANGE:
> case FALLOC_FL_PREALLOCATE:
> + case FALLOC_FL_PREALLOCATE_OLD:
> break;
> case FALLOC_FL_PUNCH_HOLE:
> if (!(mode & FALLOC_FL_KEEP_SIZE))
> diff --git a/include/linux/falloc.h b/include/linux/falloc.h
> index f6eee099b3fca..58e991ea6771f 100644
> --- a/include/linux/falloc.h
> +++ b/include/linux/falloc.h
> @@ -37,7 +37,8 @@ struct space_resv {
> FALLOC_FL_ZERO_RANGE | \
> FALLOC_FL_INSERT_RANGE | \
> FALLOC_FL_UNSHARE_RANGE | \
> - FALLOC_FL_PREALLOCATE)
> + FALLOC_FL_PREALLOCATE | \
> + FALLOC_FL_PREALLOCATE_OLD)
>
> /* on ia32 l_start is on a 32-bit boundary */
> #if defined(CONFIG_X86_64)
> diff --git a/include/uapi/linux/falloc.h b/include/uapi/linux/falloc.h
> index 7ac8ffb8e6523..49aa826ad8f8a 100644
> --- a/include/uapi/linux/falloc.h
> +++ b/include/uapi/linux/falloc.h
> @@ -78,6 +78,19 @@
> */
> #define FALLOC_FL_UNSHARE_RANGE 0x40
>
> -#define FALLOC_FL_PREALLOCATE 0x80
> +/*
> + * FALLOC_FL_PREALLOCATE tells the filesystem to allocate the range the way a
> + * write would, with mballoc preallocation, rather than trimming the request
> + * down to a single unwritten extent.
> + *
> + * Userspace may read the mode value from
> + * /sys/module/ext4/parameters/falloc_fl_preallocate.
> + *
> + * FALLOC_FL_PREALLOCATE_OLD is the value used before upstream v6.17 claimed
> + * 0x80 for FALLOC_FL_WRITE_ZEROES. It is accepted as an alias of the above,
> + * and has to be dropped before a rebase onto v6.17 or later.
> + */
> +#define FALLOC_FL_PREALLOCATE_OLD 0x80
> +#define FALLOC_FL_PREALLOCATE 0x00100000
>
> #endif /* _UAPI_FALLOC_H_ */
>
> ---
> base-commit: 3466ec0b2cdf9d49dbb36d7b5ed9b36dfb2fb04d
> change-id: 20260908-pr-khorenko-vstor-144521-falloc_fl_preallocate-cec80ce87000
>
> Best regards,
> --
> Konstantin Khorenko <khorenko@virtuozzo.com>
_______________________________________________
Devel mailing list
Devel@openvz.org
https://lists.openvz.org/mailman/listinfo/devel
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Devel] [PATCH vz10] fs: move FALLOC_FL_PREALLOCATE to a bit upstream has not taken
2026-09-08 13:38 [Devel] [PATCH vz10] fs: move FALLOC_FL_PREALLOCATE to a bit upstream has not taken Konstantin Khorenko
2026-09-08 13:43 ` Alexey Kuznetsov
@ 2026-09-08 14:25 ` Konstantin Khorenko
1 sibling, 0 replies; 3+ messages in thread
From: Konstantin Khorenko @ 2026-09-08 14:25 UTC (permalink / raw)
To: Alexey Kuznetsov, Konstantin Khorenko; +Cc: Denis V. Lunev, devel
On Tue, 08 Sep 2026 15:38:18 +0200, Konstantin Khorenko wrote:
> fs: move FALLOC_FL_PREALLOCATE to a bit upstream has not taken
Applied to branch-rh10-6.12.0-211.52.1.20.x.vz10-ovz, will be released in rh10-6.12.0-211.52.1.20.2.vz10, thanks!
[1/1] fs: move FALLOC_FL_PREALLOCATE to a bit upstream has not taken
https://bitbucket.org/virtuozzocore/vzkernel.vzs/commits/04cfdce5ceb4
--
Konstantin Khorenko <khorenko@virtuozzo.com>
_______________________________________________
Devel mailing list
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https://lists.openvz.org/mailman/listinfo/devel
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2026-09-08 13:38 [Devel] [PATCH vz10] fs: move FALLOC_FL_PREALLOCATE to a bit upstream has not taken Konstantin Khorenko
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2026-09-08 14:25 ` Konstantin Khorenko
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