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authorBoaz Harrosh <bharrosh@panasas.com>2011-10-14 15:33:51 +0200
committerBoaz Harrosh <bharrosh@panasas.com>2011-10-24 17:15:33 -0700
commit769ba8d92025fa390f3097e658b8ed6e032d68e9 (patch)
treeeec1a556d6b3796f702c96e7f97ce94ba7d9d410 /include/scsi
parenta1fec1dbbc8db974d2582e4040590cebe72171e4 (diff)
ore: RAID5 Write
This is finally the RAID5 Write support. The bigger part of this patch is not the XOR engine itself, But the read4write logic, which is a complete mini prepare_for_striping reading engine that can read scattered pages of a stripe into cache so it can be used for XOR calculation. That is, if the write was not stripe aligned. The main algorithm behind the XOR engine is the 2 dimensional array: struct __stripe_pages_2d. A drawing might save 1000 words --- __stripe_pages_2d | n = pages_in_stripe_unit; w = group_width - parity; | pages array presented to the XOR lib | | V | __1_page_stripe[0].pages --> [c0][c1]..[cw][c_par] <---| | | __1_page_stripe[1].pages --> [c0][c1]..[cw][c_par] <--- | ... | ... | __1_page_stripe[n].pages --> [c0][c1]..[cw][c_par] ^ | data added columns first then row --- The pages are put on this array columns first. .i.e: p0-of-c0, p1-of-c0, ... pn-of-c0, p0-of-c1, ... So we are doing a corner turn of the pages. Note that pages will zigzag down and left. but are put sequentially in growing order. So when the time comes to XOR the stripe, only the beginning and end of the array need be checked. We scan the array and any NULL spot will be field by pages-to-be-read. The FS that wants to support RAID5 needs to supply an operations-vector that searches a given page in cache, and specifies if the page is uptodate or need reading. All these pages to be read are put on a slave ore_io_state and synchronously read. All the pages of a stripe are read in one IO, using the scatter gather mechanism. In write we constrain our IO to only be incomplete on a single stripe. Meaning either the complete IO is within a single stripe so we might have pages to read from both beginning or end of the strip. Or we have some reading to do at beginning but end at strip boundary. The left over pages are pushed to the next IO by the API already established by previous work, where an IO offset/length combination presented to the ORE might get the length truncated and the user must re-submit the leftover pages. (Both exofs and NFS support this) But any ORE user should make it's best effort to align it's IO before hand and avoid complications. A cached ore_layout->stripe_size member can be used for that calculation. (NOTE: that ORE demands that stripe_size may not be bigger then 32bit) What else? Well read it and tell me. Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Diffstat (limited to 'include/scsi')
-rw-r--r--include/scsi/osd_ore.h9
1 files changed, 9 insertions, 0 deletions
diff --git a/include/scsi/osd_ore.h b/include/scsi/osd_ore.h
index 43821c18cd3f..f05fa826f89e 100644
--- a/include/scsi/osd_ore.h
+++ b/include/scsi/osd_ore.h
@@ -99,11 +99,17 @@ struct ore_striping_info {
unsigned dev;
unsigned par_dev;
unsigned unit_off;
+ unsigned cur_pg;
unsigned cur_comp;
};
struct ore_io_state;
typedef void (*ore_io_done_fn)(struct ore_io_state *ios, void *private);
+struct _ore_r4w_op {
+ /* @Priv given here is passed ios->private */
+ struct page * (*get_page)(void *priv, u64 page_index, bool *uptodate);
+ void (*put_page)(void *priv, struct page *page);
+};
struct ore_io_state {
struct kref kref;
@@ -139,6 +145,9 @@ struct ore_io_state {
unsigned max_par_pages;
unsigned cur_par_page;
unsigned sgs_per_dev;
+ struct __stripe_pages_2d *sp2d;
+ struct ore_io_state *ios_read_4_write;
+ const struct _ore_r4w_op *r4w;
/* Variable array of size numdevs */
unsigned numdevs;