On 20.03.23 г. 11:20 ч., Alexander Atanasov wrote:
Currently there is no way to hint the kernel to avoid triggering
page reclaims. This can be useful in networked file systems,
which can deadlock in the synchronous reclaim path and streaming
which can get unexpected jitter when a synchronouse reclaim is done.
To aid the userspace add interface to set PF_MEMALLOC, PF_MEMALLOC_NOIO,
PF_MEMALLOC_NOFS, PF_MEMALLOC_PIN flags on self.
Reading from /proc/self/memflags returns current set flags.
Writing to /proc/self/memflags sets the flags.
Flag values used are defined in the kernel header include/linux/sched.h.
https://jira.sw.ru/browse/PSBM-141577
Signed-off-by: Alexander Atanasov <alexander.atana...@virtuozzo.com>
---
fs/proc/base.c | 78 ++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 78 insertions(+)
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 0b900343aef6..8101601cc188 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1360,6 +1360,82 @@ static const struct file_operations
proc_oom_score_adj_operations = {
.llseek = default_llseek,
};
+#define MEMALLOC_FLAGS_MASK (PF_MEMALLOC | PF_MEMALLOC_NOFS | \
+ PF_MEMALLOC_NOIO | PF_MEMALLOC_PIN)
+
+static ssize_t memalloc_flags_read(struct file *file, char __user *buf,
+ size_t count, loff_t *ppos)
+{
+ struct task_struct *task = get_proc_task(file_inode(file));
+ char buffer[PROC_NUMBUF];
+ unsigned int pflags;
+ size_t len;
+
+ if (!task)
+ return -ESRCH;
nit: Looking at other functions in fs/proc/base.c that use get_proc_task
they seem to return ENOENT if NULL is returned. For the sake of
consistency I'd say change ESRCH to ENOENT.
+
+ pflags = READ_ONCE(task->flags) & MEMALLOC_FLAGS_MASK;
+ put_task_struct(task);
+ len = snprintf(buffer, sizeof(buffer), "%d\n", pflags);
Since this is really holding a mask perhaps we want an unsigned integer
or even better a hex value. Sure, non of the values in
MEMALLOC_FLAGS_MASK change bit 31 but again, let's try to be as simple
as possible". So making it a %x is the best IMO.
+ return simple_read_from_buffer(buf, count, ppos, buffer, len);
+}
+
+static ssize_t memalloc_flags_write(struct file *file, const char __user *buf,
+ size_t count, loff_t *ppos)
+{
+ struct task_struct *task = get_proc_task(file_inode(file));
+ char buffer[PROC_NUMBUF];
+ int memalloc_flags;
+ int err = -ESRCH;
Ditto
+ unsigned int pflags;
+
+ if (!task)
+ goto out;
nit: just return which then obviates the need to have a check for "if
task) under the out label, it simplifies the code overall.
+
+ if (get_exec_env() != get_ve0()) {
nit: !ve_is_super(get_exec_env()), not that it would make any material
difference, but it looks somewhat more idiomatic to me.
+ err = -EPERM;
+ goto out;
+ }
+ /*
+ * Potential issue here if task != current
+ * concurrent setting of flags need R/W_ONCE
+ * but flags are expected to change only from current
+ */
+ if (task != current) {
+ err = -EINVAL;
+ goto out;
+ }
nit: R/W_ONCE is used to prevent certain compiler optimisations and
ensure that certain accesses are atomic in the face of relaxed memory
ordering. I.e they are not a synchronization primitive. So the comment
should be rephrased to say that we can't guarantee
race-free/synchronized access to the flags.
+
+ memset(buffer, 0, sizeof(buffer));
nit: if you define the buffer as char buffer = {0} then the compiler
would generate teh code, one less line to read :D
+ if (count > sizeof(buffer) - 1)
+ count = sizeof(buffer) - 1;
nit: count = min(count, sizeof(buffer) -1)
+ if (copy_from_user(buffer, buf, count)) {
+ err = -EFAULT;
+ goto out;
+ }
+
+ err = kstrtoint(strstrip(buffer), 0, &memalloc_flags);
+ if (err)
+ goto out;
+ if (memalloc_flags & ~MEMALLOC_FLAGS_MASK) {
+ err = -EINVAL;
+ goto out;
+ }
+
+ pflags = READ_ONCE(task->flags) & ~MEMALLOC_FLAGS_MASK;
+ WRITE_ONCE(task->flags, pflags | memalloc_flags);
+out:
+ if (task)
+ put_task_struct(task);
+ return err < 0 ? err : count;
+}
+
+static const struct file_operations proc_memalloc_flags_operations = {
+ .read = memalloc_flags_read,
+ .write = memalloc_flags_write,
+ .llseek = default_llseek,
+};
+
#ifdef CONFIG_AUDIT
#define TMPBUFLEN 11
static ssize_t proc_loginuid_read(struct file * file, char __user * buf,
@@ -3400,6 +3476,7 @@ static const struct pid_entry tgid_base_stuff[] = {
ONE("oom_score", S_IRUGO, proc_oom_score),
REG("oom_adj", S_IRUGO|S_IWUSR, proc_oom_adj_operations),
REG("oom_score_adj", S_IRUGO|S_IWUSR, proc_oom_score_adj_operations),
+ REG("memalloc_flags", S_IRUGO|S_IWUSR, proc_memalloc_flags_operations),
#ifdef CONFIG_AUDIT
REG("loginuid", S_IWUSR|S_IRUGO, proc_loginuid_operations),
REG("sessionid", S_IRUGO, proc_sessionid_operations),
@@ -3749,6 +3826,7 @@ static const struct pid_entry tid_base_stuff[] = {
ONE("oom_score", S_IRUGO, proc_oom_score),
REG("oom_adj", S_IRUGO|S_IWUSR, proc_oom_adj_operations),
REG("oom_score_adj", S_IRUGO|S_IWUSR, proc_oom_score_adj_operations),
+ REG("memalloc_flags", S_IRUGO|S_IWUSR, proc_memalloc_flags_operations),
#ifdef CONFIG_AUDIT
REG("loginuid", S_IWUSR|S_IRUGO, proc_loginuid_operations),
REG("sessionid", S_IRUGO, proc_sessionid_operations),
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