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exhausted. It is possible for a bug in the code (or, theoretically, even unusual network conditions) to exhaust all possible mbufs or mbuf clusters. When this occurs, things can grind to a halt fairly quickly. However, we currently do not call mb_reclaim() unless the entire system is experiencing a low-memory condition. While it is best to try to prevent exhaustion of one of the mbuf zones, it would also be useful to have a mechanism to attempt to recover from these situations by freeing "expendable" mbufs. This patch makes two changes: a) The patch adds a generic API to the UMA zone allocator to set a function that should be called when an allocation fails because the zone limit has been reached. Because of the way this function can be called, it really should do minimal work. b) The patch uses this API to try to free mbufs when an allocation fails from one of the mbuf zones because the zone limit has been reached. The function schedules a callout to run mb_reclaim(). Differential Revision: https://reviews.freebsd.org/D3864 Reviewed by: gnn Comments by: rrs, glebius MFC after: 2 weeks Sponsored by: Juniper Networks
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