It's a write of filesystem metadata. This is likely updates to the "atime" last accessed time for every file you enumerate, which causes writes to the HFS+ catalog (as well as journal when journaling is active). You can try an experiment to see if this is the case with: $ mount -t hfs | head -1 /dev/disk0s4 on / (hfs, local, journaled) $ sudo mount -t hfs -u -o noatime /dev/disk0s4 / $ mount -t hfs | head -1 /dev/disk0s4 on / (hfs, local, journaled, noatime) $ Since this should be asynchronous, I'd be surprised if this is causing a significant performance degradation... Shantonu On Jul 6, 2012, at 2:22 PM, Dave Keck <davekeck@gmail.com> wrote:

Hey list,

I'm optimizing a program that reads image metadata using CGImageSourceCreateWithURL(). This program should strictly read from disk, but as it iterates over thousands of photos, the kernel is writing data to disk at >1 MB/sec. fs_usage reports many instances of the following:

WrMeta[asyncP] D=0x... B=0x2000 /dev/disk... 0.097343 W kernel_task

This is not the kernel paging-out to disk, as Activity Monitor reports a constant value for "Page outs" for the lifetime of the program.

What is 'WrMeta'? _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev@lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/darwin-dev/ssen%40apple.com

This email sent to ssen@apple.com

_______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev@lists.apple.com) Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app... This email sent to site_archiver@lists.apple.com