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Message-ID: <abca71ed-79c5-7485-3053-6eca0bddc53e@redhat.com>
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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