On 2017/5/4 17:03, Amir Goldstein wrote:
> On Thu, May 4, 2017 at 11:36 AM, zhangyi (F) <yi.zhang@xxxxxxxxxx> wrote:
>>
>> 2. Can we read underlying dir entry and get rid of whiteout every time for
>> the 'impure' dircetory, not execute the merged flow ? It will save
>> memory usage.
>>
> Did not understand this questions.
>
Sorry, I didn't make it clear. I mean if we set is_real = !OVL_TYPE_COPYUP()
or is_real = !OVL_TYPE_MERGE() && !ovl_dir_impure() (with optimization),
it will create ovl_dir_cache and ovl_cache_entry when we read COPYUP directory
or 'impure' dircetory in ovl_iterate() flow (as merged dir does). This will
cause bloated memory usage and some performance overhead, because this dir
is only exist in one layer(not merged), so I think it's don't need ovl_dir_cache.
(cost too much ?)
Can we find a way to avoid cache use, I find two ways(maybe too complex):
1. Make a wapper ovl_iterate_dir_impure(), it read the underlaying dir entry
and get rid of whiteout entry, and use this function to deal the COPYUP or
or 'impure' branch in ovl_iterate() like follow example:
static int ovl_iterate(struct file *file, struct dir_context *ctx)
if (od->is_real)
return iterate_dir(od->realfile, ctx);
+ else if (!OVL_TYPE_MERGE && COPYUP)
+ return ovl_iterate_dir_impure(od->realfile, ctx);
2. Add a flag in struct dir_context, let underlying filesystem to return what we
want to read, like follow example:
#define DIR_CONTEXT_HIDE_WHITEOUT (1 << 0)
struct dir_context {
const filldir_t actor;
+ unsigned int flag;
loff_t pos;
};
static int ovl_iterate(struct file *file, struct dir_context *ctx)
if (od->is_real) /* is_real = !OVL_TYPE_MERGE() */
return iterate_dir(od->realfile, ctx);
And then let underlying filesystem deal with DIR_CONTEXT_HIDE_WHITEOUT
flag. If take on this solution, we can cover all cases, OVL_TYPE_COPYUP
and pure check are also not required. It changes too greate, but has
a good expansibility (flag can be used by other demand in the future).
Thanks,
ZhangYi.
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