linux-kernel - Re: [PATCH v9 09/15] x86/sgx: Charge mem

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Date: Fri, 16 Feb 2024 07:15:59 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Haitao Huang <haitao.huang@...ux.intel.com>, jarkko@...nel.org,
 dave.hansen@...ux.intel.com, tj@...nel.org, mkoutny@...e.com,
 linux-kernel@...r.kernel.org, linux-sgx@...r.kernel.org, x86@...nel.org,
 cgroups@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 hpa@...or.com, sohil.mehta@...el.com, tim.c.chen@...ux.intel.com
Cc: zhiquan1.li@...el.com, kristen@...ux.intel.com, seanjc@...gle.com,
 zhanb@...rosoft.com, anakrish@...rosoft.com, mikko.ylinen@...ux.intel.com,
 yangjie@...rosoft.com, chrisyan@...rosoft.com
Subject: Re: [PATCH v9 09/15] x86/sgx: Charge mem_cgroup for per-cgroup
 reclamation

On 2/5/24 13:06, Haitao Huang wrote:
> @@ -414,7 +416,7 @@ static void sgx_reclaim_pages_global(void)
>  void sgx_reclaim_direct(void)
>  {
>  	if (sgx_should_reclaim(SGX_NR_LOW_PAGES))
> -		sgx_reclaim_pages_global();
> +		sgx_reclaim_pages_global(false);
>  }
>  
>  static int ksgxd(void *p)
> @@ -437,7 +439,7 @@ static int ksgxd(void *p)
>  				     sgx_should_reclaim(SGX_NR_HIGH_PAGES));
>  
>  		if (sgx_should_reclaim(SGX_NR_HIGH_PAGES))
> -			sgx_reclaim_pages_global();
> +			sgx_reclaim_pages_global(true);
>  
>  		cond_resched();
>  	}

First, I'm never a fan of random true/false or 0/1 arguments to
functions like this.  You end up having to go look at the called
function to make any sense of it.  You can either do an enum, or some
construct like this:

 		if (sgx_should_reclaim(SGX_NR_HIGH_PAGES)) {
			bool indirect = true;
			sgx_reclaim_pages_global(indirect);
		}

Yeah, it takes a few more lines but it saves you having to comment the
thing.

Does this 'indirect' change any behavior other than whether it does a
search for an mm to find a place to charge the backing storage?  Instead
of passing a flag around, why not just pass the mm?

This refactoring out of 'indirect' or passing the mm around really wants
to be in its own patch anyway.