Messages in this thread | | | Date | Thu, 08 Mar 2012 00:33:20 +0400 | From | Konstantin Khlebnikov <> | Subject | Re: Fine granularity page reclaim |
| |
Zheng Liu wrote: > > > On Monday, February 20, 2012, Konstantin Khlebnikov <khlebnikov@openvz.org <mailto:khlebnikov@openvz.org>> wrote: > > Zheng Liu wrote: > >> > >> Cc linux-kernel mailing list. > >> > >> On Sat, Feb 18, 2012 at 12:20:05AM +0400, Konstantin Khlebnikov wrote: > >>> > >>> Zheng Liu wrote: > >>>> > >>>> Hi all, > >>>> > >>>> Currently, we encounter a problem about page reclaim. In our product system, > >>>> there is a lot of applictions that manipulate a number of files. In these > >>>> files, they can be divided into two categories. One is index file, another is > >>>> block file. The number of index files is about 15,000, and the number of > >>>> block files is about 23,000 in a 2TB disk. The application accesses index > >>>> file using mmap(2), and read/write block file using pread(2)/pwrite(2). We hope > >>>> to hold index file in memory as much as possible, and it works well in Redhat > >>>> 2.6.18-164. It is about 60-70% of index files that can be hold in memory. > >>>> However, it doesn't work well in Redhat 2.6.32-133. I know in 2.6.18 that the > >>>> linux uses an active list and an inactive list to handle page reclaim, and in > >>>> 2.6.32 that they are divided into anonymous list and file list. So I am > >>>> curious about why most of index files can be hold in 2.6.18? The index file > >>>> should be replaced because mmap doesn't impact the lru list. > >>> > >>> There was my patch for fixing similar problem with shared/executable mapped pages > >>> "vmscan: promote shared file mapped pages" commit 34dbc67a644f and commit c909e99364c > >>> maybe it will help in your case. > >> > >> Hi Konstantin, > >> > >> Thank you for your reply. I have tested it in upstream kernel. These > >> patches are useful for multi-processes applications. But, in our product > >> system, there are some applications that are multi-thread. So > >> 'references_ptes> 1' cannot help these applications to hold the data in > >> memory. > > > > Ok, what if you mmap you data as executable, just to test. > > Then these pages will be activated after first touch. > > In attachment patch with per-mm flag with the same effect. > > > > Hi Konstantin, > > Sorry for the delay reply. Last two weeks I was trying these two solutions > and evaluating the impacts for the performance in our product system. > Good news is that these two solutions both work well. They can keep > mapped files in memory under mult-thread. But I have a question for > the first solution (map the file with PROT_EXEC flag). I think this way is > too tricky. As I said previously, these files that needs to be mapped only > are normal index file, and they shouldn't be mapped with PROT_EXEC flag > from the view of an application programmer. So actually the key issue is > that we should provide a mechanism, which lets different file sets can be > reclaimed separately. I am not sure whether this idea is useful or not. So > any feedbacks are welcomed.:-). Thank you. >
Sounds good. Yes, PROT_EXEC isn't very usable and secure, per-mm flag not very flexible too. I prefer setting some kind of memory pressure priorities for each vma and inode. Probably we can sort vma and inodes into different cgroup-like sets and balance memory pressure between them. Maybe someone was thought about it...
| |