lkml.org 
[lkml]   [2018]   [Jul]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH v6 0/7] fs/dcache: Track & limit # of negative dentries
    From
    Date
    On Fri, 2018-07-13 at 10:36 +1000, Dave Chinner wrote:
    > On Thu, Jul 12, 2018 at 12:57:15PM -0700, James Bottomley wrote:
    > > What surprises me most about this behaviour is the steadiness of
    > > the page cache ... I would have thought we'd have shrunk it
    > > somewhat given the intense call on the dcache.
    >
    > Oh, good, the page cache vs superblock shrinker balancing still
    > protects the working set of each cache the way it's supposed to
    > under heavy single cache pressure. :)

    Well, yes, but my expectation is most of the page cache is clean, so
    easily reclaimable. I suppose part of my surprise is that I expected
    us to reclaim the clean caches first before we started pushing out the
    dirty stuff and reclaiming it. I'm not saying it's a bad thing, just
    saying I didn't expect us to make such good decisions under the
    parameters of this test.

    > Keep in mind that the amount of work slab cache shrinkers perform is
    > directly proportional to the amount of page cache reclaim that is
    > performed and the size of the slab cache being reclaimed.  IOWs,
    > under a "single cache pressure" workload we should be directing
    > reclaim work to the huge cache creating the pressure and do very
    > little reclaim from other caches....

    That definitely seems to happen. The thing I was most surprised about
    is the steady pushing of anonymous objects to swap. I agree the dentry
    cache doesn't seem to be growing hugely after the initial jump, so it
    seems to be the largest source of reclaim.

    > [ What follows from here is conjecture, but is based on what I've
    > seen in the past 10+ years on systems with large numbers of negative
    > dentries and fragmented dentry/inode caches. ]

    OK, so I fully agree with the concern about pathological object vs page
    freeing problems (I referred to it previously). However, I did think
    the compaction work that's been ongoing in mm was supposed to help
    here?

    James

    \
     
     \ /
      Last update: 2018-07-15 22:07    [W:3.277 / U:0.212 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site