Messages in this thread | | | Date | Sat, 20 Jan 2007 12:26:13 +0800 | From | "Aubrey Li" <> | Subject | Re: [RPC][PATCH 2.6.20-rc5] limit total vfs page cache |
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On 1/20/07, Nick Piggin <nickpiggin@yahoo.com.au> wrote: > Aubrey Li wrote: > > > So what's the right way to limit pagecache? > > Probably something a lot more complicated... if you can say there > is a "right way". > > >> Secondly, your patch isn't actually very good. It unconditionally > >> shrinks memory to below the given % mark each time a pagecache alloc > >> occurs, regardless of how much pagecache is in the system. Effectively > >> that seems to just reduce the amount of memory available to the system. > > > > > > It doesn't reduce the amount of memory available to the system. It > > just reduce the amount of memory available to the page cache. So that > > page cache is limited and the reserved memory can be allocated by the > > application. > > But the patch doesn't do that, as I explained.
I'm not sure you read the correct patch. Let me explain the logic again.
assume: min = 123pages pagecache_reserved = 200 pages
if( alloc_flags & ALLOC_PAGECACHE) watermark = min + pagecache_reserved ( 323 pages) else watermark = min ( 123 pages)
So if request pagecache, when free pages < 323 pages, reclaim is triggered. But at this time if request memory not pagecache, reclaim will be triggered when free pages < 123 as the present reclaimer does.
I verified it on my side, why do you think it doesn't work properly?
> > >> Luckily, there are actually good, robust solutions for your higher > >> order allocation problem. Do higher order allocations at boot time, > >> modifiy userspace applications, or set up otherwise-unused, or easily > >> reclaimable reserve pools for higher order allocations. I don't > >> understand why you are so resistant to all of these approaches? > >> > > > > I think we have explained the reason too much. We are working on > > no-mmu arch and provide a platform running linux to our customer. They > > are doing very good things like mplayer, asterisk, ip camera, etc on > > our platform, some applications was migrated from mmu arch. I think > > that means in some cases no-mmu arch is somewhat better than mmu arch. > > So we are taking effort to make the migration smooth or make no-mmu > > linux stronger. > > It's no way to let our customer modify their applications, we also > > unwilling to do it. And we have not an existing mechanism to set up a > > pools for the complex applications. So I'm trying to do some coding > > hack in the kernel to satisfy these kinds of requirement. > > Oh, maybe you misunderstand the reserve pools idea: that is an entirely > kernel based solution where you can preallocate a large, contiguous > pool of memory at boot time which you can use to satisfy your nommu > higher order anonymous memory allocations. > > This is something that will not get fragmented by pagecache, nor will > it get fragmented by any other page allocation, slab allocation. Tt is > a pretty good solution provided that you size the pool correctly for > your application's needs. >
So if application malloc(1M), how does kernel know to allocate reserved pool not from buddy system? I didn't see any special code about this. Is there any doc or example?
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