Messages in this thread | | | From | KOSAKI Motohiro <> | Subject | Re: [PATCH 4/7] nandsim: Don't use PF_MEMALLOC | Date | Wed, 25 Nov 2009 09:42:16 +0900 (JST) |
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> ext KOSAKI Motohiro wrote: > > Hi > > > > Thank you for this useful comments. > > > >>> I vaguely remember Adrian (CCed) did this on purpose. This is for the > >>> case when nandsim emulates NAND flash on top of a file. So there are 2 > >>> file-systems involved: one sits on top of nandsim (e.g. UBIFS) and the > >>> other owns the file which nandsim uses (e.g., ext3). > >>> > >>> And I really cannot remember off the top of my head why he needed > >>> PF_MEMALLOC, but I think Adrian wanted to prevent the direct reclaim > >>> path to re-enter, say UBIFS, and cause deadlock. But I'd thing that all > >>> the allocations in vfs_read()/vfs_write() should be GFP_NOFS, so that > >>> should not be a probelm? > >>> > >> Yes it needs PF_MEMALLOC to prevent deadlock because there can be a > >> file system on top of nandsim which, in this case, is on top of another > >> file system. > >> > >> I do not see how mempools will help here. > >> > >> Please offer an alternative solution. > > > > I have few questions. > > > > Can you please explain more detail? Another stackable filesystam > > (e.g. ecryptfs) don't have such problem. Why nandsim have its issue? > > What lock cause deadlock? > > The file systems are not stacked. One is over nandsim, which nandsim > does not know about because it is just a lowly NAND device, and, with > the file cache option, one file system below to provide the file cache. > > The deadlock is the kernel writing out dirty pages to the top file system > which writes to nandsim which writes to the bottom file system which > allocates memory which causes dirty pages to be written out to the top > file system, which tries to write to nandsim => deadlock.
You mean you want to prevent pageout() instead reclaim itself? Dropping filecache seems don't make recursive call, right?
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