linux-kernel - Re: [PATCH 04/22] staging: lustre: osc: handle osc eviction correctly

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Date:   Mon, 5 Dec 2016 18:03:58 -0500
From:   Oleg Drokin <oleg.drokin@...el.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     James Simmons <jsimmons@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <devel@...verdev.osuosl.org>,
        Andreas Dilger <andreas.dilger@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jinshan Xiong <jinshan.xiong@...el.com>,
        Lustre Development List <lustre-devel@...ts.lustre.org>
Subject: Re: [PATCH 04/22] staging: lustre: osc: handle osc eviction correctly


On Dec 5, 2016, at 3:55 PM, Dan Carpenter wrote:

> On Fri, Dec 02, 2016 at 07:53:11PM -0500, James Simmons wrote:
>> @@ -3183,8 +3182,10 @@ static int discard_cb(const struct lu_env *env, struct cl_io *io,
>> 	/* page is top page. */
>> 	info->oti_next_index = osc_index(ops) + 1;
>> 	if (cl_page_own(env, io, page) == 0) {
>> -		KLASSERT(ergo(page->cp_type == CPT_CACHEABLE,
>> -			      !PageDirty(cl_page_vmpage(page))));
>> +		if (!ergo(page->cp_type == CPT_CACHEABLE,
>> +			  !PageDirty(cl_page_vmpage(page))))
>> +			CL_PAGE_DEBUG(D_ERROR, env, page,
>> +				      "discard dirty page?\n");
> 
> 
> I don't understand the point of the ergo macro.  There are way too many
> double negatives (some of them hidden for my small brain).  How is that
> simpler than just writing it out:
> 
> 	if (page->cp_type == CPT_CACHEABLE &&
> 	    PageDirty(cl_page_vmpage(page))
> 		 CL_PAGE_DEBUG(D_ERROR, env, page, "discard dirty page?\n");

I guess it makes it sound chic or something?
I am not a huge fan of it either, esp. in a case like this, though
it might be somewhat more convenient in assertions (where this is converted from).