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Kernel: Avoid allocating under spinlock in ProcessGroup::find_or_create

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Avoid allocating while holding the g_process_groups_lock spinlock, it's
a pattern that has a negative effect on performance and scalability,
especially given that it is a global lock, reachable by all processes.
This commit is contained in:
Brian Gianforcaro 2021-05-19 22:16:41 -07:00 committed by Andreas Kling
parent bb91bed576
commit e95eb7a51d
Notes: sideshowbarker 2024-07-18 17:43:45 +09:00 
Author: https://github.com/bgianfo
Commit: https://github.com/SerenityOS/serenity/commit/e95eb7a51d8
Pull-request: https://github.com/SerenityOS/serenity/pull/7243
Reviewed-by: https://github.com/awesomekling
2 changed files with 17 additions and 2 deletions
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17
Kernel/ProcessGroup.cpp
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@ -30,18 +30,31 @@ RefPtr<ProcessGroup> ProcessGroup::create(ProcessGroupID pgid)
RefPtr<ProcessGroup> ProcessGroup::find_or_create(ProcessGroupID pgid)
{
// Avoid allocating under spinlock, this compromises by wasting the
// allocation when we race with another process to see if they have
// already created a process group.
auto process_group = adopt_ref_if_nonnull(new ProcessGroup(pgid));
ScopedSpinLock lock(g_process_groups_lock);
if (auto existing = from_pgid(pgid))
if (auto existing = from_pgid_nolock(pgid))
return existing.release_nonnull();
return create(pgid);
if (!process_group)
return {};
g_process_groups->prepend(process_group);
return process_group;
}
RefPtr<ProcessGroup> ProcessGroup::from_pgid(ProcessGroupID pgid)
{
ScopedSpinLock lock(g_process_groups_lock);
return from_pgid_nolock(pgid);
}
RefPtr<ProcessGroup> ProcessGroup::from_pgid_nolock(ProcessGroupID pgid)
{
VERIFY(g_process_groups_lock.own_lock());
for (auto& group : *g_process_groups) {
if (group.pgid() == pgid)
return &group;

2
Kernel/ProcessGroup.h
View file

@ -40,6 +40,8 @@ private:
{
}
static RefPtr<ProcessGroup> from_pgid_nolock(ProcessGroupID);
ProcessGroup* m_prev { nullptr };
ProcessGroup* m_next { nullptr };