Re: [PATCH 2/9] nilfs2: add simple cache for modifications to SUFILE
On Tue, 24 Feb 2015 20:01:37 +0100, Andreas Rohner wrote:
> This patch adds a simple, small cache that can be used to accumulate
> modifications to SUFILE entries. This is for example useful for
> keeping track of reclaimable blocks, because most of the
> modifications consist of small increments or decrements. By adding
> these up and temporarily storing them in a small cache, the
> performance can be improved. Additionally lock contention is
> reduced.
>
> Signed-off-by: Andreas Rohner
> ---
> fs/nilfs2/sufile.c | 178
> +
> fs/nilfs2/sufile.h | 44 +
> 2 files changed, 222 insertions(+)
>
> diff --git a/fs/nilfs2/sufile.c b/fs/nilfs2/sufile.c
> index 1e8cac6..a369c30 100644
> --- a/fs/nilfs2/sufile.c
> +++ b/fs/nilfs2/sufile.c
> @@ -1168,6 +1168,184 @@ out_sem:
> }
>
> /**
> + * nilfs_sufile_mc_init - inits segusg modification cache
> + * @mc: modification cache
> + * @capacity: maximum capacity of the mod cache
> + *
> + * Description: Allocates memory for an array of nilfs_sufile_mod structures
> + * according to @capacity. This memory must be freed with
> + * nilfs_sufile_mc_destroy().
> + *
> + * Return Value: On success, 0 is returned. On error, one of the following
> + * negative error codes is returned.
> + *
> + * %-ENOMEM - Insufficient amount of memory available.
> + *
> + * %-EINVAL - Invalid capacity.
> + */
> +int nilfs_sufile_mc_init(struct nilfs_sufile_mod_cache *mc, size_t capacity)
> +{
> + mc->mc_capacity = capacity;
> + if (!capacity)
> + return -EINVAL;
> +
> + mc->mc_mods = kmalloc(capacity * sizeof(struct nilfs_sufile_mod),
> + GFP_KERNEL);
GFP_NOFS must be used instead of GFP_KERNEL to avoid initiating other
filesystem operations.
The abbreviation "mc" is not good, which is already used as the
abbreviation of "minimum clean" in userland.
> + if (!mc->mc_mods)
> + return -ENOMEM;
> +
> + mc->mc_size = 0;
> +
> + return 0;
> +}
> +
> +/**
> + * nilfs_sufile_mc_add - add signed value to segusg modification cache
> + * @mc: modification cache
> + * @segnum: segment number
> + * @value: signed value (can be positive and negative)
> + *
> + * Description: nilfs_sufile_mc_add() tries to add a pair of @segnum and
> + * @value to the modification cache. If the cache already contains a
> + * segment number equal to @segnum, then @value is simply added to the
> + * existing value. This way thousands of small modifications can be
> + * accumulated into one value. If @segnum cannot be found and the
> + * capacity allows it, a new element is added to the cache. If the
> + * capacity is reached an error value is returned.
> + *
> + * Return Value: On success, 0 is returned. On error, one of the following
> + * negative error codes is returned.
> + *
> + * %-ENOSPC - The mod cache has reached its capacity and must be flushed.
> + */
> +static inline int nilfs_sufile_mc_add(struct nilfs_sufile_mod_cache *mc,
> + __u64 segnum, __s64 value)
> +{
> + struct nilfs_sufile_mod *mods = mc->mc_mods;
> + int i;
> +
> + for (i = 0; i < mc->mc_size; ++i, ++mods) {
> + if (mods->m_segnum == segnum) {
> + mods->m_value += value;
> + return 0;
> + }
> + }
> +
> + if (mc->mc_size < mc->mc_capacity) {
> + mods->m_segnum = segnum;
> + mods->m_value = value;
> + mc->mc_size++;
> + return 0;
> + }
> +
> + return -ENOSPC;
> +}
> +
> +/**
> + * nilfs_sufile_mc_clear - set mc_size to 0
> + * @mc: modification cache
> + *
> + * Description: nilfs_sufile_mc_clear() sets mc_size to 0, which enables
> + * nilfs_sufile_mc_add() to overwrite the elements in @mc.
> + */
> +static inline void nilfs_sufile_mc_clear(struct nilfs_sufile_mod_cache *mc)
> +{
> + mc->mc_size = 0;
> +}
> +
> +/**
> + * nilfs_sufile_mc_reset - clear cache and add one element
> + * @mc: modification cache
> + * @segnum: segment number
> + * @value: signed value (can be positive and negative)
> + *
> + * Description: Clears the modification cache in @mc and adds a new pair of
> + * @segnum and @value to it at the same time.
> + */
> +static inline void nilfs_sufile_mc_reset(struct nilfs_sufile_mod_cache *mc,
> + __u64 segnum, __s64 value)
> +{
> + struct nilfs_sufile_mod *mods = mc->mc_mods;
> +
> + mods->m_segnum = segnum;
> + mods->m_value = value;
> + mc->mc_size = 1;
> +}
The name of this function is confusing. Actual meaning of this
function is "reset" and "add", and that can be replaced with mc_clear
and mc_add. Remove this function to simplify interface.
Regards,
Ryusuke Konishi
> +/**
> + * nilfs_sufile_mc_flush - flush modification cache
> + * @sufile: inode of segment usage file
> + * @mc: modification cache
> + * @dofunc: primitive operation for the update
> + *
[PATCH 2/9] nilfs2: add simple cache for modifications to SUFILE
This patch adds a simple, small cache that can be used to accumulate
modifications to SUFILE entries. This is for example useful for
keeping track of reclaimable blocks, because most of the
modifications consist of small increments or decrements. By adding
these up and temporarily storing them in a small cache, the
performance can be improved. Additionally lock contention is
reduced.
Signed-off-by: Andreas Rohner
---
fs/nilfs2/sufile.c | 178 +
fs/nilfs2/sufile.h | 44 +
2 files changed, 222 insertions(+)
diff --git a/fs/nilfs2/sufile.c b/fs/nilfs2/sufile.c
index 1e8cac6..a369c30 100644
--- a/fs/nilfs2/sufile.c
+++ b/fs/nilfs2/sufile.c
@@ -1168,6 +1168,184 @@ out_sem:
}
/**
+ * nilfs_sufile_mc_init - inits segusg modification cache
+ * @mc: modification cache
+ * @capacity: maximum capacity of the mod cache
+ *
+ * Description: Allocates memory for an array of nilfs_sufile_mod structures
+ * according to @capacity. This memory must be freed with
+ * nilfs_sufile_mc_destroy().
+ *
+ * Return Value: On success, 0 is returned. On error, one of the following
+ * negative error codes is returned.
+ *
+ * %-ENOMEM - Insufficient amount of memory available.
+ *
+ * %-EINVAL - Invalid capacity.
+ */
+int nilfs_sufile_mc_init(struct nilfs_sufile_mod_cache *mc, size_t capacity)
+{
+ mc->mc_capacity = capacity;
+ if (!capacity)
+ return -EINVAL;
+
+ mc->mc_mods = kmalloc(capacity * sizeof(struct nilfs_sufile_mod),
+ GFP_KERNEL);
+ if (!mc->mc_mods)
+ return -ENOMEM;
+
+ mc->mc_size = 0;
+
+ return 0;
+}
+
+/**
+ * nilfs_sufile_mc_add - add signed value to segusg modification cache
+ * @mc: modification cache
+ * @segnum: segment number
+ * @value: signed value (can be positive and negative)
+ *
+ * Description: nilfs_sufile_mc_add() tries to add a pair of @segnum and
+ * @value to the modification cache. If the cache already contains a
+ * segment number equal to @segnum, then @value is simply added to the
+ * existing value. This way thousands of small modifications can be
+ * accumulated into one value. If @segnum cannot be found and the
+ * capacity allows it, a new element is added to the cache. If the
+ * capacity is reached an error value is returned.
+ *
+ * Return Value: On success, 0 is returned. On error, one of the following
+ * negative error codes is returned.
+ *
+ * %-ENOSPC - The mod cache has reached its capacity and must be flushed.
+ */
+static inline int nilfs_sufile_mc_add(struct nilfs_sufile_mod_cache *mc,
+ __u64 segnum, __s64 value)
+{
+ struct nilfs_sufile_mod *mods = mc->mc_mods;
+ int i;
+
+ for (i = 0; i < mc->mc_size; ++i, ++mods) {
+ if (mods->m_segnum == segnum) {
+ mods->m_value += value;
+ return 0;
+ }
+ }
+
+ if (mc->mc_size < mc->mc_capacity) {
+ mods->m_segnum = segnum;
+ mods->m_value = value;
+ mc->mc_size++;
+ return 0;
+ }
+
+ return -ENOSPC;
+}
+
+/**
+ * nilfs_sufile_mc_clear - set mc_size to 0
+ * @mc: modification cache
+ *
+ * Description: nilfs_sufile_mc_clear() sets mc_size to 0, which enables
+ * nilfs_sufile_mc_add() to overwrite the elements in @mc.
+ */
+static inline void nilfs_sufile_mc_clear(struct nilfs_sufile_mod_cache *mc)
+{
+ mc->mc_size = 0;
+}
+
+/**
+ * nilfs_sufile_mc_reset - clear cache and add one element
+ * @mc: modification cache
+ * @segnum: segment number
+ * @value: signed value (can be positive and negative)
+ *
+ * Description: Clears the modification cache in @mc and adds a new pair of
+ * @segnum and @value to it at the same time.
+ */
+static inline void nilfs_sufile_mc_reset(struct nilfs_sufile_mod_cache *mc,
+__u64 segnum, __s64 value)
+{
+ struct nilfs_sufile_mod *mods = mc->mc_mods;
+
+ mods->m_segnum = segnum;
+ mods->m_value = value;
+ mc->mc_size = 1;
+}
+
+/**
+ * nilfs_sufile_mc_flush - flush modification cache
+ * @sufile: inode of segment usage file
+ * @mc: modification cache
+ * @dofunc: primitive operation for the update
+ *
+ * Description: nilfs_sufile_mc_flush() flushes the cached modifications
+ * and applies them to the segment usages on disk. It persists the cached
+ * changes, by calling @dofunc for every element in the cache. @dofunc also
+ * determines the interpretation of the cached values and how they should
+ * be applied to the corresponding segment usage entries.
+ *
+ * Return Value: On success, zero is returned. On error, one of the
+ * following negative error codes is returned.
+ *
+ * %-EIO - I/O error.
+ *
+ * %-ENOMEM - Insufficient amount of memory available.
+ *
+ * %-ENOENT - Given segment usage is in hole block
+ *
+ * %-EINVAL - Invalid segment usage number
+ */
+stat
