• Mel Gorman's avatar
    x86, mm: trace when an IPI is about to be sent · 5b74283a
    Mel Gorman authored
    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
    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
    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: default avatarMel Gorman <mgorman@suse.de>
    Reviewed-by: default avatarRik van Riel <riel@redhat.com>
    Reviewed-by: default avatarDave Hansen <dave.hansen@intel.com>
    Acked-by: default avatarIngo Molnar <mingo@kernel.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
tlb.h 1.42 KB