> From: Seth Jennings [mailto:sjenning@xxxxxxxxxxxxxxxxxx] > Subject: Re: [PATCHv3 5/6] zswap: add to mm/ > > On 01/29/2013 12:27 AM, Minchan Kim wrote: > > First feeling is it's simple and nice approach. > > Although we have some problems to decide policy, it could solve by later patch > > so I hope we make basic infrasture more solid by lots of comment. > > Thanks very much for the review! > > > > Another question. > > > > What's the benefit of using mempool for zsmalloc? > > As you know, zsmalloc doesn't use mempool as default. > > I guess you see some benefit. if so, zram could be changed. > > If we can change zsmalloc's default scheme to use mempool, > > all of customer of zsmalloc could be enhanced, too. > > In the case of zswap, through experimentation, I found that adding a > mempool behind the zsmalloc pool added some elasticity to the pool. > Fewer stores failed if we kept a small reserve of pages around instead > of having to go back to the buddy allocator who, under memory > pressure, is more likely to reject our request. > > I don't see this situation being applicable to all zsmalloc users > however. I don't think we want incorporate it directly into zsmalloc > for now. The ability to register custom page alloc/free functions at > pool creation time allows users to do something special, like back > with a mempool, if they want to do that. (sorry, still catching up on backlog after being gone last week) IIUC, by using mempool, you are essentially setting aside a special cache of pageframes that only zswap can use (or other users of mempool, I don't know what other subsystems use it). So one would expect that fewer stores would fail if more pageframes are available to zswap, the same as if you had increased zswap_max_pool_percent by some small fraction. But by setting those pageframes aside, you are keeping them from general use, which may be a use with a higher priority as determined by the mm system. This seems wrong to me. Should every subsystem hide a bunch of pageframes away in case it might need them? Or am I missing something? Dan _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/devel
