From: Igor Fedotov <igor.fedotov@croit.io>
Date: Tue, 15 Jul 2025 20:47:57 +0000 (+0300)
Subject: blk/kernel: cap single discard request's length
X-Git-Tag: v21.0.0~256^2~123^2
X-Git-Url: http://git-server-git.apps.pok.os.sepia.ceph.com/?a=commitdiff_plain;h=f232623747256b3612f4e61d276cfa5d8ae9df33;p=ceph.git

blk/kernel: cap single discard request's length

Signed-off-by: Igor Fedotov <igor.fedotov@croit.io>
---

diff --git a/src/blk/kernel/KernelDevice.cc b/src/blk/kernel/KernelDevice.cc
index 11db95b5f4f6..a455fb18bcb9 100644
--- a/src/blk/kernel/KernelDevice.cc
+++ b/src/blk/kernel/KernelDevice.cc
@@ -1196,10 +1196,23 @@ int KernelDevice::_discard(uint64_t offset, uint64_t len)
 	       << dendl;
     return 0;
   }
-  dout(10) << __func__
-           << " 0x" << std::hex << offset << "~" << len << std::dec
-           << dendl;
-  r = BlkDev{fd_directs[WRITE_LIFE_NOT_SET]}.discard((int64_t)offset, (int64_t)len);
+  uint64_t max_len = cct->_conf->bdev_max_discard_length;
+  if (max_len) {
+    while (len > 0 && r == 0) {
+      auto l = std::min(max_len, len);
+      dout(10) << __func__
+               << " 0x" << std::hex << offset << "~" << l << std::dec
+               << dendl;
+      r = BlkDev{fd_directs[WRITE_LIFE_NOT_SET]}.discard((int64_t)offset, (int64_t)l);
+      offset += l;
+      len -= l;
+    }
+  } else {
+    dout(10) << __func__
+             << " 0x" << std::hex << offset << "~" << len << std::dec
+             << dendl;
+    r = BlkDev{fd_directs[WRITE_LIFE_NOT_SET]}.discard((int64_t)offset, (int64_t)len);
+  }
   return r;
 }
 
diff --git a/src/common/options/global.yaml.in b/src/common/options/global.yaml.in
index 490d5c4edd40..1f2bae5e410e 100644
--- a/src/common/options/global.yaml.in
+++ b/src/common/options/global.yaml.in
@@ -4167,6 +4167,16 @@ options:
   - runtime
   see_also:
   - bdev_async_discard_threads
+- name: bdev_max_discard_length
+  desc: maximum length of a single discard request
+  type: uint
+  level: advanced
+  default: 2147483648
+  with_legacy: true
+  flags:
+  - runtime
+  see_also:
+  - bdev_enable_discard
 - name: bdev_flock_retry_interval
   type: float
   level: advanced