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Re: [PATCH] xen/page_alloc: Simplify domain_adjust_tot_pages


  • To: Alejandro Vallejo <alejandro.vallejo@xxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Wed, 26 Feb 2025 15:02:44 +0100
  • Autocrypt: addr=jbeulich@xxxxxxxx; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL
  • Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Wed, 26 Feb 2025 14:02:54 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 24.02.2025 14:27, Alejandro Vallejo wrote:
> @@ -504,17 +502,16 @@ unsigned long domain_adjust_tot_pages(struct domain *d, 
> long pages)
>          goto out;
>  
>      spin_lock(&heap_lock);
> -    /* adjust domain outstanding pages; may not go negative */
> -    dom_before = d->outstanding_pages;
> -    dom_after = dom_before - pages;
> -    BUG_ON(dom_before < 0);
> -    dom_claimed = dom_after < 0 ? 0 : dom_after;
> -    d->outstanding_pages = dom_claimed;
> -    /* flag accounting bug if system outstanding_claims would go negative */
> -    sys_before = outstanding_claims;
> -    sys_after = sys_before - (dom_before - dom_claimed);
> -    BUG_ON(sys_after < 0);
> -    outstanding_claims = sys_after;
> +    BUG_ON(outstanding_claims < d->outstanding_pages);
> +    if ( pages > 0 && d->outstanding_pages < pages )

The lhs isn't needed, is it? d->outstanding_pages is an unsigned quantity,
after all. Else dropping the earlier of the two BUG_ON() wouldn't be quite
right.

> +    {
> +        /* `pages` exceeds the domain's outstanding count. Zero it out. */
> +        outstanding_claims -= d->outstanding_pages;
> +        d->outstanding_pages = 0;
> +    } else {

Nit: Braces on their own lines please.

In any event - yes, this reads quite a bit easier after the adjustment.

With the adjustments (happy to make while committing, so long as you agree)
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan

> +        outstanding_claims -= pages;
> +        d->outstanding_pages -= pages;
> +    }
>      spin_unlock(&heap_lock);
>  
>  out:




 


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