Re: Re: question about striped_read

[majianpeng <majianpeng@gmail.com>]

>On Mon, Jul 29, 2013 at 11:00 AM, majianpeng <majianpeng@gmail.com> wrote:
>>
>> [snip]
>> >I don't think the later was_short can handle the hole case. For the hole case,
>> >we should try reading next strip object instead of return. how about
>> >below patch.
>> >
>> Hi Yan,
>>         i uesed this demo to test hole case.
>> dd if=/dev/urandom bs=4096 count=2 of=file_with_holes
>> dd if=/dev/urandom bs=4096 seek=7 count=2 of=file_with_holes
>>
>> dd if=file_with_holes of=/dev/null bs=16k count=1 iflag=direct
>> Using the dynamic_debug in striped_read,  the message are:
>> >[ 8743.663499] ceph:           file.c:350  : striped_read 0~16384 (read 0) got 16384
>> >[ 8743.663502] ceph:           file.c:390  : striped_read returns 16384
>> From the messages, we can see it can't hit the short-read.
>> For the ceph-file-hole, how does the ceph handle?
>> Or am i missing something?
>
>the default strip size is 4M, all data are written to the first object
>in your test case.
>could you try something like below.
>
>dd if=/dev/urandom bs=1M count=2 of=file_with_holes
>dd if=/dev/urandom bs=1M count=2 seek=4 of=file_with_holes conv=notrunc
>dd if=file_with_holes bs=8M >/dev/null
>

From above test, i think your patch is right.
Although, the original code can work but it  call multi striped_read.
As your said for stripe short-read,it doesn't make sense to return rather than reading next stripe.
But can you add some comments for this?
The short-read reasongs are two:EOF or hit-hole.
But for hit-hole there are some differents case. For that i don't know.

Thanks!
Jianpeng Ma
>Regards
>Yan, Zheng
>
>
>>
>>
>> Thanks!
>> Jianpeng Ma
>>
>> >Regards
>> >Yan, Zheng
>> >---
>> >diff --git a/fs/ceph/file.c b/fs/ceph/file.c
>> >index 271a346..6ca2921 100644
>> >--- a/fs/ceph/file.c
>> >+++ b/fs/ceph/file.c
>> >@@ -350,16 +350,17 @@ more:
>> >            ret, hit_stripe ? " HITSTRIPE" : "", was_short ? " SHORT" : "");
>> >
>> >       if (ret > 0) {
>> >-              int didpages = (page_align + ret) >> PAGE_CACHE_SHIFT;
>> >+              int didpages = (page_align + this_len) >> PAGE_CACHE_SHIFT;
>> >
>> >-              if (read < pos - off) {
>> >-                      dout(" zero gap %llu to %llu\n", off + read, pos);
>> >-                      ceph_zero_page_vector_range(page_align + read,
>> >-                                                  pos - off - read, pages);
>> >+              if (was_short) {
>> >+                      dout(" zero gap %llu to %llu\n",
>> >+                           pos + ret, pos + this_len);
>> >+                      ceph_zero_page_vector_range(page_align + ret,
>> >+                                                  this_len - ret, page_pos);
>> >               }
>> >-              pos += ret;
>> >+              pos += this_len;
>> >               read = pos - off;
>> >-              left -= ret;
>> >+              left -= this_len;
>> >               page_pos += didpages;
>> >               pages_left -= didpages;
>> >
Thanks!
Jianpeng Ma
>On Mon, Jul 29, 2013 at 11:00 AM, majianpeng <majianpeng@gmail.com> wrote:
>>
>> [snip]
>> >I don't think the later was_short can handle the hole case. For the hole case,
>> >we should try reading next strip object instead of return. how about
>> >below patch.
>> >
>> Hi Yan,
>>         i uesed this demo to test hole case.
>> dd if=/dev/urandom bs=4096 count=2 of=file_with_holes
>> dd if=/dev/urandom bs=4096 seek=7 count=2 of=file_with_holes
>>
>> dd if=file_with_holes of=/dev/null bs=16k count=1 iflag=direct
>> Using the dynamic_debug in striped_read,  the message are:
>> >[ 8743.663499] ceph:           file.c:350  : striped_read 0~16384 (read 0) got 16384
>> >[ 8743.663502] ceph:           file.c:390  : striped_read returns 16384
>> From the messages, we can see it can't hit the short-read.
>> For the ceph-file-hole, how does the ceph handle?
>> Or am i missing something?
>
>the default strip size is 4M, all data are written to the first object
>in your test case.
>could you try something like below.
>
>dd if=/dev/urandom bs=1M count=2 of=file_with_holes
>dd if=/dev/urandom bs=1M count=2 seek=4 of=file_with_holes conv=notrunc
>dd if=file_with_holes bs=8M >/dev/null
>
>Regards
>Yan, Zheng
>
>
>>
>>
>> Thanks!
>> Jianpeng Ma
>>
>> >Regards
>> >Yan, Zheng
>> >---
>> >diff --git a/fs/ceph/file.c b/fs/ceph/file.c
>> >index 271a346..6ca2921 100644
>> >--- a/fs/ceph/file.c
>> >+++ b/fs/ceph/file.c
>> >@@ -350,16 +350,17 @@ more:
>> >            ret, hit_stripe ? " HITSTRIPE" : "", was_short ? " SHORT" : "");
>> >
>> >       if (ret > 0) {
>> >-              int didpages = (page_align + ret) >> PAGE_CACHE_SHIFT;
>> >+              int didpages = (page_align + this_len) >> PAGE_CACHE_SHIFT;
>> >
>> >-              if (read < pos - off) {
>> >-                      dout(" zero gap %llu to %llu\n", off + read, pos);
>> >-                      ceph_zero_page_vector_range(page_align + read,
>> >-                                                  pos - off - read, pages);
>> >+              if (was_short) {
>> >+                      dout(" zero gap %llu to %llu\n",
>> >+                           pos + ret, pos + this_len);
>> >+                      ceph_zero_page_vector_range(page_align + ret,
>> >+                                                  this_len - ret, page_pos);
>> >               }
>> >-              pos += ret;
>> >+              pos += this_len;
>> >               read = pos - off;
>> >-              left -= ret;
>> >+              left -= this_len;
>> >               page_pos += didpages;
>> >               pages_left -= didpages;
>> >