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SubjectRe: [PATCH 4/7] nandsim: Don't use PF_MEMALLOC
Bityutskiy Artem (Nokia-D/Helsinki) wrote:
> On Tue, 2009-11-17 at 16:19 +0900, KOSAKI Motohiro wrote:
>> Non MM subsystem must not use PF_MEMALLOC. Memory reclaim need few
>> memory, anyone must not prevent it. Otherwise the system cause
>> mysterious hang-up and/or OOM Killer invokation.
>>
>> Cc: David Woodhouse <David.Woodhouse@intel.com>
>> Cc: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
>> Cc: linux-mtd@lists.infradead.org
>> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
>> ---
>> drivers/mtd/nand/nandsim.c | 22 ++--------------------
>> 1 files changed, 2 insertions(+), 20 deletions(-)
>>
>> diff --git a/drivers/mtd/nand/nandsim.c b/drivers/mtd/nand/nandsim.c
>> index cd0711b..97a8bbb 100644
>> --- a/drivers/mtd/nand/nandsim.c
>> +++ b/drivers/mtd/nand/nandsim.c
>> @@ -1322,34 +1322,18 @@ static int get_pages(struct nandsim *ns, struct file *file, size_t count, loff_t
>> return 0;
>> }
>>
>> -static int set_memalloc(void)
>> -{
>> - if (current->flags & PF_MEMALLOC)
>> - return 0;
>> - current->flags |= PF_MEMALLOC;
>> - return 1;
>> -}
>> -
>> -static void clear_memalloc(int memalloc)
>> -{
>> - if (memalloc)
>> - current->flags &= ~PF_MEMALLOC;
>> -}
>> -
>> static ssize_t read_file(struct nandsim *ns, struct file *file, void *buf, size_t count, loff_t *pos)
>> {
>> mm_segment_t old_fs;
>> ssize_t tx;
>> - int err, memalloc;
>> + int err;
>>
>> err = get_pages(ns, file, count, *pos);
>> if (err)
>> return err;
>> old_fs = get_fs();
>> set_fs(get_ds());
>> - memalloc = set_memalloc();
>> tx = vfs_read(file, (char __user *)buf, count, pos);
>> - clear_memalloc(memalloc);
>> set_fs(old_fs);
>> put_pages(ns);
>> return tx;
>> @@ -1359,16 +1343,14 @@ static ssize_t write_file(struct nandsim *ns, struct file *file, void *buf, size
>> {
>> mm_segment_t old_fs;
>> ssize_t tx;
>> - int err, memalloc;
>> + int err;
>>
>> err = get_pages(ns, file, count, *pos);
>> if (err)
>> return err;
>> old_fs = get_fs();
>> set_fs(get_ds());
>> - memalloc = set_memalloc();
>> tx = vfs_write(file, (char __user *)buf, count, pos);
>> - clear_memalloc(memalloc);
>> set_fs(old_fs);
>> put_pages(ns);
>> return tx;PF_MEMALLOC,
>
> 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.


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