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Date: Sun, 8 Nov 2020 21:17:29 -0500 From: Waiman Long <longman@...hat.com> To: Jan Kara <jack@...e.cz> Cc: Amir Goldstein <amir73il@...il.com>, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, Luca BRUNO <lucab@...hat.com> Subject: Re: [PATCH v3] inotify: Increase default inotify.max_user_watches limit to 1048576 On 10/30/20 6:57 AM, Jan Kara wrote: > 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@...hat.com> > 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? Yes, it will be easier to read to use clamp() here. Will send out v4 withat those changes. Thanks, Longman
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