Messages in this thread | | | Date | Wed, 25 Nov 2009 09:13:22 +0200 | From | Adrian Hunter <> | Subject | Re: [PATCH 4/7] nandsim: Don't use PF_MEMALLOC |
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KOSAKI Motohiro wrote: >> 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?
Yes
> Dropping filecache seems don't make recursive call, right?
Yes
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