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    SubjectRe: [PATCH 4/7] nandsim: Don't use PF_MEMALLOC
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    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;

    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?

    --
    Best Regards,
    Artem Bityutskiy (Артём Битюцкий)

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