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cache: release lock before clearing

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Clearing the FD cache could trigger a lot of inode evicts in the kernel,
which will block the cache entry destructors called by map::clear().
This prevents any cache lookups or new file opens while it happens.

Move the map to an auto variable and destroy it after releasing the
mutex lock.  This probably has the same net result (all the bees threads
will be blocked in the kernel instead of on a bees mutex), but at least
the problem is outside of userspace now.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>
This commit is contained in:
Zygo Blaxell 2018-02-07 23:14:38 -05:00
parent 8f0e88433e
commit 86afa69cd1
1 changed files with 4 additions and 2 deletions
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6
include/crucible/cache.h
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@ -122,7 +122,7 @@ namespace crucible {
// Splice new node into list
Value *last_bp = m_last->bp;
THROW_CHECK0(runtime_error, last_bp);
// New elemnt points to both ends of list
// New element points to both ends of list
vp->fp = m_last;
vp->bp = last_bp;
// Insert vp as fp from the end of the list
@ -158,8 +158,10 @@ namespace crucible {
void
LRUCache<Return, Arguments...>::clear()
{
// Move the map onto the stack, then destroy it after we've released the lock.
decltype(m_map) new_map;
unique_lock<mutex> lock(m_mutex);
m_map.clear();
m_map.swap(new_map);
m_last = nullptr;
}