linux-kernel - Re: [PATCH] ib/core: not to set page dirty bit if it's already set.

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Message-ID: <20170519130541.GA8017@infradead.org>
Date:   Fri, 19 May 2017 06:05:41 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Qing Huang <qing.huang@...cle.com>
Cc:     linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        dledford@...hat.com, sean.hefty@...el.com, artemyko@...lanox.com,
        linux-mm@...ck.org
Subject: Re: [PATCH] ib/core: not to set page dirty bit if it's already set.

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

> 
> Signed-off-by: Qing Huang <qing.huang@...cle.com>
> ---
>  drivers/infiniband/core/umem.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
> index 3dbf811..21e60b1 100644
> --- a/drivers/infiniband/core/umem.c
> +++ b/drivers/infiniband/core/umem.c
> @@ -58,7 +58,7 @@ static void __ib_umem_release(struct ib_device *dev, struct ib_umem *umem, int d
>  	for_each_sg(umem->sg_head.sgl, sg, umem->npages, i) {
>  
>  		page = sg_page(sg);
> -		if (umem->writable && dirty)
> +		if (!PageDirty(page) && umem->writable && dirty)
>  			set_page_dirty_lock(page);
>  		put_page(page);
>  	}
> -- 
> 2.9.3
> 
> --
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---end quoted text---