Messages in this thread | | | From | Qing Huang <> | Subject | Re: [PATCH] ib/core: not to set page dirty bit if it's already set. | Date | Tue, 23 May 2017 14:39:38 -0700 |
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On 5/23/2017 12:42 AM, Christoph Hellwig wrote: > On Mon, May 22, 2017 at 04:43:57PM -0700, Qing Huang wrote: >> On 5/19/2017 6:05 AM, Christoph Hellwig wrote: >>> On Thu, May 18, 2017 at 04:33:53PM -0700, Qing Huang wrote: >>>> This change will optimize kernel memory deregistration operations. >>>> __ib_umem_release() used to call set_page_dirty_lock() against every >>>> writable page in its memory region. Its purpose is to keep data >>>> synced between CPU and DMA device when swapping happens after mem >>>> deregistration ops. Now we choose not to set page dirty bit if it's >>>> already set by kernel prior to calling __ib_umem_release(). This >>>> reduces memory deregistration time by half or even more when we ran >>>> application simulation test program. >>> As far as I can tell this code doesn't even need set_page_dirty_lock >>> and could just use set_page_dirty >> It seems that set_page_dirty_lock has been used here for more than 10 years. >> Don't know the original purpose. Maybe it was used to prevent races between >> setting dirty bits and swapping out pages? > I suspect copy & paste. Or maybe I don't actually understand the > explanation of set_page_dirty vs set_page_dirty_lock enough. But > I'd rather not hack around the problem. > -- I think there are two parts here. First part is that we don't need to set the dirty bit if it's already set. Second part is whether we use set_page_dirty or set_page_dirty_lock to set dirty bits.
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