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On 10.09.2019 10:35 Damien Le Moal
wrote:
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. I had issues with this as well, and work on this is appreciated!
In my case it is a loop block device on a fuse file system. Sorry, I have no idea about the current rationale, but wouldn't it be better to have a
way to mask a set of block devices/file systems not to
write-back to in a thread. So in my case I'd specify that the
fuse daemon threads cannot write-back to the file system and
loop device running on top of the fuse file system, while all
other block devices/file systems can be write-back to (causing
less swapping/OOM issues). 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)
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