On Thu 29-10-20 15:42:56, Waiman Long wrote:
> The default value of inotify.max_user_watches sysctl parameter was set
> to 8192 since the introduction of the inotify feature in 2005 by
> commit 0eeca28300df ("[PATCH] inotify"). Today this value is just too
> small for many modern usage. As a result, users have to explicitly set
> it to a larger value to make it work.
>
> After some searching around the web, these are the
> inotify.max_user_watches values used by some projects:
> - vscode: 524288
> - dropbox support: 100000
> - users on stackexchange: 12228
> - lsyncd user: 2000000
> - code42 support: 1048576
> - monodevelop: 16384
> - tectonic: 524288
> - openshift origin: 65536
>
> Each watch point adds an inotify_inode_mark structure to an inode to
> be watched. It also pins the watched inode.
>
> Modeled after the epoll.max_user_watches behavior to adjust the default
> value according to the amount of addressable memory available, make
> inotify.max_user_watches behave in a similar way to make it use no more
> than 1% of addressable memory within the range [8192, 1048576].
>
> For 64-bit archs, inotify_inode_mark plus 2 vfs inode have a size that
> is a bit over 1 kbytes (1284 bytes with my x86-64 config). That means
> a system with 128GB or more memory will likely have the maximum value
> of 1048576 for inotify.max_user_watches. This default should be big
> enough for most use cases.
>
> [v3: increase inotify watch cost as suggested by Amir and Honza]
>
> Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
Overall this looks fine. Some remaining nits below.
> diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
> index 186722ba3894..f8065eda3a02 100644
> --- a/fs/notify/inotify/inotify_user.c
> +++ b/fs/notify/inotify/inotify_user.c
> @@ -37,6 +37,15 @@
>
> #include <asm/ioctls.h>
>
> +/*
> + * An inotify watch requires allocating an inotify_inode_mark structure as
> + * well as pinning the watched inode. Doubling the size of a VFS inode
> + * should be more than enough to cover the additional filesystem inode
> + * size increase.
> + */
> +#define INOTIFY_WATCH_COST (sizeof(struct inotify_inode_mark) + \
> + 2 * sizeof(struct inode))
> +
> /* configurable via /proc/sys/fs/inotify/ */
> static int inotify_max_queued_events __read_mostly;
>
> @@ -801,6 +810,18 @@ SYSCALL_DEFINE2(inotify_rm_watch, int, fd, __s32, wd)
> */
> static int __init inotify_user_setup(void)
> {
> + unsigned int watches_max;
> + struct sysinfo si;
> +
> + si_meminfo(&si);
> + /*
> + * Allow up to 1% of addressible memory to be allocated for inotify
^^^^ addressable
> + * watches (per user) limited to the range [8192, 1048576].
> + */
> + watches_max = (((si.totalram - si.totalhigh) / 100) << PAGE_SHIFT) /
> + INOTIFY_WATCH_COST;
^^^ So for machines with > 1TB of memory
watches_max would overflow. So you probably need to use ulong for that.
> + watches_max = min(1048576U, max(watches_max, 8192U));
^^^ use clamp() here?
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
