zram: write incompressible pages to backing device

This patch enables write IO to transfer data to backing device.  For
that, it implements write_to_bdev function which creates new bio and
chaining with parent bio to make the parent bio asynchrnous.

For rw_page which don't have parent bio, it submit owned bio and handle
IO completion by zram_page_end_io.

Also, this patch defines new flag ZRAM_WB to mark written page for later
read IO.

[xieyisheng1@huawei.com: fix typo in comment]
  Link: http://lkml.kernel.org/r/1502707447-6944-2-git-send-email-xieyisheng1@huawei.com
Link: http://lkml.kernel.org/r/1498459987-24562-8-git-send-email-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Yisheng Xie <xieyisheng1@huawei.com>
Cc: Juneho Choi <juno.choi@lge.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 103 insertions, 13 deletions

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 8975f75f113d..195b3372241c 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -445,9 +445,76 @@ static void put_entry_bdev(struct zram *zram, unsigned long entry)
         WARN_ON_ONCE(!was_set);
 }
 
+void zram_page_end_io(struct bio *bio)
+{
+        struct page *page = bio->bi_io_vec[0].bv_page;
+
+        page_endio(page, op_is_write(bio_op(bio)),
+                        blk_status_to_errno(bio->bi_status));
+        bio_put(bio);
+}
+
+static int write_to_bdev(struct zram *zram, struct bio_vec *bvec,
+                                        u32 index, struct bio *parent,
+                                        unsigned long *pentry)
+{
+        struct bio *bio;
+        unsigned long entry;
+
+        bio = bio_alloc(GFP_ATOMIC, 1);
+        if (!bio)
+                return -ENOMEM;
+
+        entry = get_entry_bdev(zram);
+        if (!entry) {
+                bio_put(bio);
+                return -ENOSPC;
+        }
+
+        bio->bi_iter.bi_sector = entry * (PAGE_SIZE >> 9);
+        bio->bi_bdev = zram->bdev;
+        if (!bio_add_page(bio, bvec->bv_page, bvec->bv_len,
+                                        bvec->bv_offset)) {
+                bio_put(bio);
+                put_entry_bdev(zram, entry);
+                return -EIO;
+        }
+
+        if (!parent) {
+                bio->bi_opf = REQ_OP_WRITE | REQ_SYNC;
+                bio->bi_end_io = zram_page_end_io;
+        } else {
+                bio->bi_opf = parent->bi_opf;
+                bio_chain(bio, parent);
+        }
+
+        submit_bio(bio);
+        *pentry = entry;
+
+        return 0;
+}
+
+static void zram_wb_clear(struct zram *zram, u32 index)
+{
+        unsigned long entry;
+
+        zram_clear_flag(zram, index, ZRAM_WB);
+        entry = zram_get_element(zram, index);
+        zram_set_element(zram, index, 0);
+        put_entry_bdev(zram, entry);
+}
+
 #else
 static bool zram_wb_enabled(struct zram *zram) { return false; }
 static inline void reset_bdev(struct zram *zram) {};
+static int write_to_bdev(struct zram *zram, struct bio_vec *bvec,
+                                        u32 index, struct bio *parent,
+                                        unsigned long *pentry)
+
+{
+        return -EIO;
+}
+static void zram_wb_clear(struct zram *zram, u32 index) {}
 #endif
 
 
@@ -672,7 +739,13 @@ static bool zram_meta_alloc(struct zram *zram, u64 disksize)
  */
 static void zram_free_page(struct zram *zram, size_t index)
 {
-        unsigned long handle = zram_get_handle(zram, index);
+        unsigned long handle;
+
+        if (zram_wb_enabled(zram) && zram_test_flag(zram, index, ZRAM_WB)) {
+                zram_wb_clear(zram, index);
+                atomic64_dec(&zram->stats.pages_stored);
+                return;
+        }
 
         /*
          * No memory is allocated for same element filled pages.
@@ -686,6 +759,7 @@ static void zram_free_page(struct zram *zram, size_t index)
                 return;
         }
 
+        handle = zram_get_handle(zram, index);
         if (!handle)
                 return;
 
@@ -770,7 +844,8 @@ out:
         return ret;
 }
 
-static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index)
+static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
+                                u32 index, struct bio *bio)
 {
         int ret = 0;
         unsigned long alloced_pages;
@@ -781,6 +856,7 @@ static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index)
         struct page *page = bvec->bv_page;
         unsigned long element = 0;
         enum zram_pageflags flags = 0;
+        bool allow_wb = true;
 
         mem = kmap_atomic(page);
         if (page_same_filled(mem, &element)) {
@@ -805,8 +881,20 @@ compress_again:
                 return ret;
         }
 
-        if (unlikely(comp_len > max_zpage_size))
+        if (unlikely(comp_len > max_zpage_size)) {
+                if (zram_wb_enabled(zram) && allow_wb) {
+                        zcomp_stream_put(zram->comp);
+                        ret = write_to_bdev(zram, bvec, index, bio, &element);
+                        if (!ret) {
+                                flags = ZRAM_WB;
+                                ret = 1;
+                                goto out;
+                        }
+                        allow_wb = false;
+                        goto compress_again;
+                }
                 comp_len = PAGE_SIZE;
+        }
 
         /*
          * handle allocation has 2 paths:
@@ -866,10 +954,11 @@ out:
          */
         zram_slot_lock(zram, index);
         zram_free_page(zram, index);
-        if (flags == ZRAM_SAME) {
-                zram_set_flag(zram, index, ZRAM_SAME);
+
+        if (flags) {
+                zram_set_flag(zram, index, flags);
                 zram_set_element(zram, index, element);
-        } else {
+        }  else {
                 zram_set_handle(zram, index, handle);
                 zram_set_obj_size(zram, index, comp_len);
         }
@@ -881,7 +970,7 @@ out:
 }
 
 static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
-                                u32 index, int offset)
+                                u32 index, int offset, struct bio *bio)
 {
         int ret;
         struct page *page = NULL;
@@ -914,7 +1003,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
                 vec.bv_offset = 0;
         }
 
-        ret = __zram_bvec_write(zram, &vec, index);
+        ret = __zram_bvec_write(zram, &vec, index, bio);
 out:
         if (is_partial_io(bvec))
                 __free_page(page);
@@ -965,7 +1054,7 @@ static void zram_bio_discard(struct zram *zram, u32 index,
  * Returns 1 if IO request was successfully submitted.
  */
 static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
-                        int offset, bool is_write)
+                        int offset, bool is_write, struct bio *bio)
 {
         unsigned long start_time = jiffies;
         int rw_acct = is_write ? REQ_OP_WRITE : REQ_OP_READ;
@@ -980,7 +1069,7 @@ static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
                 flush_dcache_page(bvec->bv_page);
         } else {
                 atomic64_inc(&zram->stats.num_writes);
-                ret = zram_bvec_write(zram, bvec, index, offset);
+                ret = zram_bvec_write(zram, bvec, index, offset, bio);
         }
 
         generic_end_io_acct(rw_acct, &zram->disk->part0, start_time);
@@ -1024,7 +1113,7 @@ static void __zram_make_request(struct zram *zram, struct bio *bio)
                         bv.bv_len = min_t(unsigned int, PAGE_SIZE - offset,
                                                         unwritten);
                         if (zram_bvec_rw(zram, &bv, index, offset,
-                                        op_is_write(bio_op(bio))) < 0)
+                                        op_is_write(bio_op(bio)), bio) < 0)
                                 goto out;
 
                         bv.bv_offset += bv.bv_len;
@@ -1098,7 +1187,7 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector,
         bv.bv_len = PAGE_SIZE;
         bv.bv_offset = 0;
 
-        ret = zram_bvec_rw(zram, &bv, index, offset, is_write);
+        ret = zram_bvec_rw(zram, &bv, index, offset, is_write, NULL);
 out:
         /*
          * If I/O fails, just return error(ie, non-zero) without
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 707aec0a2681..31762db861e3 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -60,9 +60,10 @@ static const size_t max_zpage_size = PAGE_SIZE / 4 * 3;
 
 /* Flags for zram pages (table[page_no].value) */
 enum zram_pageflags {
-        /* Page consists entirely of zeros */
+        /* Page consists the same element */
         ZRAM_SAME = ZRAM_FLAG_SHIFT,
         ZRAM_ACCESS,    /* page is now accessed */
+        ZRAM_WB,        /* page is stored on backing_device */
 
         __NR_ZRAM_PAGEFLAGS,
 };