Re: [PATCH v1 3/5] mem-pool: fill out functionality

[Jameson Miller <jameson.miller81@gmail.com>]

On 04/20/2018 07:21 PM, Jonathan Tan wrote:
> On Tue, 17 Apr 2018 16:34:42 +0000
> Jameson Miller <jamill@microsoft.com> wrote:
> 
>> @@ -19,8 +19,27 @@ struct mem_pool {
>>   
>>   	/* The total amount of memory allocated by the pool. */
>>   	size_t pool_alloc;
>> +
>> +	/*
>> +	 * Array of pointers to "custom size" memory allocations.
>> +	 * This is used for "large" memory allocations.
>> +	 * The *_end variables are used to track the range of memory
>> +	 * allocated.
>> +	 */
>> +	void **custom, **custom_end;
>> +	int nr, nr_end, alloc, alloc_end;
> 
> This seems overly complicated - the struct mem_pool already has a linked
> list of pages, so couldn't you create a custom page and insert it behind
> the current front page instead whenever you needed a large-size page?

Yes - that is another option. However, the linked list of pages includes 
memory that *could* have space for an allocation, while the "custom" 
region will never have left over memory that can be used for other 
allocations. When searching pages for memory to satisfy a request, there 
is no reason to search through the "custom" pages. There is a trade-off 
between complexity and implementation, so I am open to suggestions.

This was discussed in [1], where it originally was implemented closer to 
what you describe here.

> 
> Also, when combining, there could be some wasted space on one of the
> pages. I'm not sure if that's worth calling out, though.
> 

Yes, we bring over the whole page. However, these pages are now 
available for new allocations.

[1]
https://public-inbox.org/git/xmqqk1u2k91l.fsf@gitster-ct.c.googlers.com/