On April 1, 2025 12:30:46 AM PDT, Yafang Shao <laoar.shao@xxxxxxxxx> wrote: >While investigating a kcompactd 100% CPU utilization issue in production, I >observed frequent costly high-order (order-6) page allocations triggered by >proc file reads from monitoring tools. This can be reproduced with a simple >test case: > > fd = open(PROC_FILE, O_RDONLY); > size = read(fd, buff, 256KB); > close(fd); > >Although we should modify the monitoring tools to use smaller buffer sizes, >we should also enhance the kernel to prevent these expensive high-order >allocations. > >Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx> >Cc: Josef Bacik <josef@xxxxxxxxxxxxxx> >--- > fs/proc/proc_sysctl.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > >diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c >index cc9d74a06ff0..c53ba733bda5 100644 >--- a/fs/proc/proc_sysctl.c >+++ b/fs/proc/proc_sysctl.c >@@ -581,7 +581,15 @@ static ssize_t proc_sys_call_handler(struct kiocb *iocb, struct iov_iter *iter, > error = -ENOMEM; > if (count >= KMALLOC_MAX_SIZE) > goto out; >- kbuf = kvzalloc(count + 1, GFP_KERNEL); >+ >+ /* >+ * Use vmalloc if the count is too large to avoid costly high-order page >+ * allocations. >+ */ >+ if (count < (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) >+ kbuf = kvzalloc(count + 1, GFP_KERNEL); Why not move this check into kvmalloc family? >+ else >+ kbuf = vmalloc(count + 1); You dropped the zeroing. This must be vzalloc. > if (!kbuf) > goto out; > Alternatively, why not force count to be <PAGE_SIZE? What uses >PAGE_SIZE writes in proc/sys? -Kees -- Kees Cook
