From 7ad5d56bd0893df98a89cfe1d936177f1cebf257 Mon Sep 17 00:00:00 2001
From: Vitaliy Filippov <vitalif@yourcmc.ru>
Date: Tue, 21 Apr 2026 01:53:00 +0300
Subject: [PATCH] Do not use too small end of the RDMA send buffer

---
 src/client/msgr_rdma.cpp | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/src/client/msgr_rdma.cpp b/src/client/msgr_rdma.cpp
index 9831a1de..9354bf3a 100644
--- a/src/client/msgr_rdma.cpp
+++ b/src/client/msgr_rdma.cpp
@@ -590,7 +590,36 @@ void osd_messenger_t::try_send_rdma(osd_client_t *cl)
     while (!rc->send_out_full && copied > 0 && rc->cur_send < rc->max_send)
     {
         dst = (uint8_t*)rc->send_out.buf + rc->send_out_pos;
-        dst_len = (rc->send_out_pos < rc->send_out_size ? rc->send_out_size-rc->send_out_pos : rc->send_done_pos-rc->send_out_pos);
+        if (rc->send_out_pos >= rc->send_done_pos)
+        {
+            dst_len = rc->send_out_size-rc->send_out_pos;
+            if (dst_len < 4096)
+            {
+                // free end of the buffer is too small, skip
+                rc->send_out_pos = 0;
+                if (rc->send_out_pos >= rc->send_done_pos)
+                    rc->send_out_full = true;
+                if (!rc->send_sizes.size())
+                {
+                    rc->send_done_pos += dst_len;
+                    rc->send_out_full = false;
+                    if (rc->send_done_pos == rc->send_out_size)
+                        rc->send_done_pos = 0;
+                }
+                else
+                    rc->send_sizes.back() += dst_len;
+                continue;
+            }
+        }
+        else
+        {
+            dst_len = rc->send_done_pos-rc->send_out_pos;
+            if (dst_len < 4096)
+            {
+                // too small buffer, stop
+                break;
+            }
+        }
         if (dst_len > rc->max_msg)
             dst_len = rc->max_msg;
         copied = copy_ops_to(cl, dst, dst_len);