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When unmapping pages it is necessary to flush the TLB. If that page was
accessed by another CPU then an IPI is used to flush the remote CPU. That
is a lot of IPIs if kswapd is scanning and unmapping >100K pages per
second.
There already is a window between when a page is unmapped and when it is
TLB flushed. This series increases the window so multiple pages can be
flushed using a single IPI. This should be safe or the kernel is hosed
already.
Patch 1 simply made the rest of the series easier to write as ftrace
could identify all the senders of TLB flush IPIS.
Patch 2 tracks what CPUs potentially map a PFN and then sends an IPI
to flush the entire TLB.
Patch 3 tracks when there potentially are writable TLB entries that
need to be batched differently
Patch 4 increases SWAP_CLUSTER_MAX to further batch flushes
The performance impact is documented in the changelogs but in the optimistic
case on a 4-socket machine the full series reduces interrupts from 900K
interrupts/second to 60K interrupts/second.
This patch (of 4):
It is easy to trace when an IPI is received to flush a TLB but harder to
detect what event sent it. This patch makes it easy to identify the
source of IPIs being transmitted for TLB flushes on x86.
Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
64 lines
1.4 KiB
C
64 lines
1.4 KiB
C
#undef TRACE_SYSTEM
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#define TRACE_SYSTEM tlb
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#if !defined(_TRACE_TLB_H) || defined(TRACE_HEADER_MULTI_READ)
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#define _TRACE_TLB_H
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#include <linux/mm_types.h>
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#include <linux/tracepoint.h>
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#define TLB_FLUSH_REASON \
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EM( TLB_FLUSH_ON_TASK_SWITCH, "flush on task switch" ) \
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EM( TLB_REMOTE_SHOOTDOWN, "remote shootdown" ) \
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EM( TLB_LOCAL_SHOOTDOWN, "local shootdown" ) \
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EM( TLB_LOCAL_MM_SHOOTDOWN, "local mm shootdown" ) \
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EMe( TLB_REMOTE_SEND_IPI, "remote ipi send" )
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/*
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* First define the enums in TLB_FLUSH_REASON to be exported to userspace
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* via TRACE_DEFINE_ENUM().
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*/
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#undef EM
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#undef EMe
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#define EM(a,b) TRACE_DEFINE_ENUM(a);
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#define EMe(a,b) TRACE_DEFINE_ENUM(a);
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TLB_FLUSH_REASON
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/*
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* Now redefine the EM() and EMe() macros to map the enums to the strings
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* that will be printed in the output.
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*/
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#undef EM
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#undef EMe
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#define EM(a,b) { a, b },
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#define EMe(a,b) { a, b }
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TRACE_EVENT_CONDITION(tlb_flush,
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TP_PROTO(int reason, unsigned long pages),
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TP_ARGS(reason, pages),
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TP_CONDITION(cpu_online(smp_processor_id())),
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TP_STRUCT__entry(
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__field( int, reason)
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__field(unsigned long, pages)
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),
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TP_fast_assign(
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__entry->reason = reason;
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__entry->pages = pages;
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),
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TP_printk("pages:%ld reason:%s (%d)",
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__entry->pages,
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__print_symbolic(__entry->reason, TLB_FLUSH_REASON),
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__entry->reason)
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);
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#endif /* _TRACE_TLB_H */
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/* This part must be outside protection */
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#include <trace/define_trace.h>
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