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 1t+7+Pzb 5mL+41gDGj/qGJiN2uGtTMbbRj8v1EkWMMFfUaZVgLEDW+2y4bYMALXBLtEuWjrgZ/N7mu68K2TrkQNKpRQq4sZ0WxwsaTZE86jhoEN0G13Jiew8QISP5wlCi56pYTIJiwyf041Fo0uNDMFQFhknGf+eg2Q== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Apr 01, 2025 at 07:01:04AM -0700, Kees Cook wrote: > > > On April 1, 2025 12:30:46 AM PDT, Yafang Shao 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 > >Cc: Josef Bacik > >--- > > 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? Hmm should this check really be in kvmalloc family? I don't think users would expect kvmalloc() to implictly decide on using vmalloc() without trying kmalloc() first, just because it's a high-order allocation. > >+ 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 writes in proc/sys? > > -Kees > > -- > Kees Cook -- Cheers, Harry (formerly known as Hyeonggon)