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    SubjectRe: [PATCH v12 07/20] dax,ext2: Replace ext2_clear_xip_target with dax_clear_blocks
    On Fri, 24 Oct 2014 17:20:39 -0400 Matthew Wilcox <matthew.r.wilcox@intel.com> wrote:

    > This is practically generic code; other filesystems will want to call
    > it from other places, but there's nothing ext2-specific about it.
    >
    > Make it a little more generic by allowing it to take a count of the number
    > of bytes to zero rather than fixing it to a single page. Thanks to Dave
    > Hansen for suggesting that I need to call cond_resched() if zeroing more
    > than one page.
    >
    > ...
    >
    > --- a/fs/dax.c
    > +++ b/fs/dax.c
    > @@ -20,8 +20,45 @@
    > #include <linux/fs.h>
    > #include <linux/genhd.h>
    > #include <linux/mutex.h>
    > +#include <linux/sched.h>
    > #include <linux/uio.h>
    >
    > +int dax_clear_blocks(struct inode *inode, sector_t block, long size)
    > +{
    > + struct block_device *bdev = inode->i_sb->s_bdev;
    > + sector_t sector = block << (inode->i_blkbits - 9);
    > +
    > + might_sleep();
    > + do {
    > + void *addr;
    > + unsigned long pfn;
    > + long count;
    > +
    > + count = bdev_direct_access(bdev, sector, &addr, &pfn, size);
    > + if (count < 0)
    > + return count;
    > + BUG_ON(size < count);
    > + while (count > 0) {
    > + unsigned pgsz = PAGE_SIZE - offset_in_page(addr);
    > + if (pgsz > count)
    > + pgsz = count;
    > + if (pgsz < PAGE_SIZE)
    > + memset(addr, 0, pgsz);
    > + else
    > + clear_page(addr);

    Are there any cache issues in all this code? flush_dcache_page(addr)?

    > + addr += pgsz;
    > + size -= pgsz;
    > + count -= pgsz;
    > + BUG_ON(pgsz & 511);
    > + sector += pgsz / 512;
    > + cond_resched();
    > + }
    > + } while (size);
    > +
    > + return 0;
    > +}
    > +EXPORT_SYMBOL_GPL(dax_clear_blocks);
    >
    > ...
    >


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