Mike, On 2019/09/09 19:26, Mike Christie wrote: > Forgot to cc linux-mm. > > On 09/09/2019 11:28 AM, Mike Christie wrote: >> There are several storage drivers like dm-multipath, iscsi, and nbd that >> have userspace components that can run in the IO path. For example, >> iscsi and nbd's userspace deamons may need to recreate a socket and/or >> send IO on it, and dm-multipath's daemon multipathd may need to send IO >> to figure out the state of paths and re-set them up. >> >> In the kernel these drivers have access to GFP_NOIO/GFP_NOFS and the >> memalloc_*_save/restore functions to control the allocation behavior, >> but for userspace we would end up hitting a allocation that ended up >> writing data back to the same device we are trying to allocate for. >> >> This patch allows the userspace deamon to set the PF_MEMALLOC* flags >> through procfs. It currently only supports PF_MEMALLOC_NOIO, but >> depending on what other drivers and userspace file systems need, for >> the final version I can add the other flags for that file or do a file >> per flag or just do a memalloc_noio file. Awesome. That probably will be the perfect solution for the problem we hit with tcmu-runner a while back (please see this thread: https://www.spinics.net/lists/linux-fsdevel/msg148912.html). I think we definitely need nofs as well for dealing with cases where the backend storage for the user daemon is a file. I will give this patch a try as soon as possible (I am traveling currently). Best regards. >> >> Signed-off-by: Mike Christie <mchristi@xxxxxxxxxx> >> --- >> Documentation/filesystems/proc.txt | 6 ++++ >> fs/proc/base.c | 53 ++++++++++++++++++++++++++++++ >> 2 files changed, 59 insertions(+) >> >> diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt >> index 99ca040e3f90..b5456a61a013 100644 >> --- a/Documentation/filesystems/proc.txt >> +++ b/Documentation/filesystems/proc.txt >> @@ -46,6 +46,7 @@ Table of Contents >> 3.10 /proc/<pid>/timerslack_ns - Task timerslack value >> 3.11 /proc/<pid>/patch_state - Livepatch patch operation state >> 3.12 /proc/<pid>/arch_status - Task architecture specific information >> + 3.13 /proc/<pid>/memalloc - Control task's memory reclaim behavior >> >> 4 Configuring procfs >> 4.1 Mount options >> @@ -1980,6 +1981,11 @@ Example >> $ cat /proc/6753/arch_status >> AVX512_elapsed_ms: 8 >> >> +3.13 /proc/<pid>/memalloc - Control task's memory reclaim behavior >> +----------------------------------------------------------------------- >> +A value of "noio" indicates that when a task allocates memory it will not >> +reclaim memory that requires starting phisical IO. >> + >> Description >> ----------- >> >> diff --git a/fs/proc/base.c b/fs/proc/base.c >> index ebea9501afb8..c4faa3464602 100644 >> --- a/fs/proc/base.c >> +++ b/fs/proc/base.c >> @@ -1223,6 +1223,57 @@ static const struct file_operations proc_oom_score_adj_operations = { >> .llseek = default_llseek, >> }; >> >> +static ssize_t memalloc_read(struct file *file, char __user *buf, size_t count, >> + loff_t *ppos) >> +{ >> + struct task_struct *task; >> + ssize_t rc = 0; >> + >> + task = get_proc_task(file_inode(file)); >> + if (!task) >> + return -ESRCH; >> + >> + if (task->flags & PF_MEMALLOC_NOIO) >> + rc = simple_read_from_buffer(buf, count, ppos, "noio", 4); >> + put_task_struct(task); >> + return rc; >> +} >> + >> +static ssize_t memalloc_write(struct file *file, const char __user *buf, >> + size_t count, loff_t *ppos) >> +{ >> + struct task_struct *task; >> + char buffer[5]; >> + int rc = count; >> + >> + memset(buffer, 0, sizeof(buffer)); >> + if (count != sizeof(buffer) - 1) >> + return -EINVAL; >> + >> + if (copy_from_user(buffer, buf, count)) >> + return -EFAULT; >> + buffer[count] = '\0'; >> + >> + task = get_proc_task(file_inode(file)); >> + if (!task) >> + return -ESRCH; >> + >> + if (!strcmp(buffer, "noio")) { >> + task->flags |= PF_MEMALLOC_NOIO; >> + } else { >> + rc = -EINVAL; >> + } >> + >> + put_task_struct(task); >> + return rc; >> +} >> + >> +static const struct file_operations proc_memalloc_operations = { >> + .read = memalloc_read, >> + .write = memalloc_write, >> + .llseek = default_llseek, >> +}; >> + >> #ifdef CONFIG_AUDIT >> #define TMPBUFLEN 11 >> static ssize_t proc_loginuid_read(struct file * file, char __user * buf, >> @@ -3097,6 +3148,7 @@ static const struct pid_entry tgid_base_stuff[] = { >> #ifdef CONFIG_PROC_PID_ARCH_STATUS >> ONE("arch_status", S_IRUGO, proc_pid_arch_status), >> #endif >> + REG("memalloc", S_IRUGO|S_IWUSR, proc_memalloc_operations), >> }; >> >> static int proc_tgid_base_readdir(struct file *file, struct dir_context *ctx) >> @@ -3487,6 +3539,7 @@ static const struct pid_entry tid_base_stuff[] = { >> #ifdef CONFIG_PROC_PID_ARCH_STATUS >> ONE("arch_status", S_IRUGO, proc_pid_arch_status), >> #endif >> + REG("memalloc", S_IRUGO|S_IWUSR, proc_memalloc_operations), >> }; >> >> static int proc_tid_base_readdir(struct file *file, struct dir_context *ctx) >> > > -- Damien Le Moal Western Digital Research
