Re: [PATCH v4 2/3] mm/free_pcppages_bulk: do not hold lock when picking pages to free

[Aaron Lu]

On Thu, Mar 22, 2018 at 08:17:19AM -0700, Matthew Wilcox wrote:
> On Tue, Mar 13, 2018 at 11:34:53AM +0800, Aaron Lu wrote:
> > I wish there is a data structure that has the flexibility of list while
> > at the same time we can locate the Nth element in the list without the
> > need to iterate. That's what I'm looking for when developing clustered
> > allocation for order 0 pages. In the end, I had to use another place to
> > record where the Nth element is. I hope to send out v2 of that RFC
> > series soon but I'm still collecting data for it. I would appreciate if
> > people could take a look then :-)
> 
> Sorry, I missed this.  There is such a data structure -- the IDR, or
> possibly a bare radix tree, or we can build a better data structure on
> top of the radix tree (I talked about one called the XQueue a while ago).
> 
> The IDR will automatically grow to whatever needed size, it stores
> pointers, you can find out quickly where the last allocated index is,
> you can remove from the middle of the array.  Disadvantage is that it
> requires memory allocation to store the array of pointers, *but* it
> can always hold at least one entry.  So if you have no memory, you can
> always return the one element in your IDR to the free pool and allocate
> from that page.

Thanks for the pointer, will take a look later.
Currently I'm focusing on finding real workloads that have zone lock
contention issue.