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fix: remove double RMSNorm on B/C in MambaInnerFn.backward at checkpoint_lvl=1 #939

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fix: remove double RMSNorm on B/C in MambaInnerFn.backward at checkpoint_lvl=1 #939

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14 changes: 0 additions & 14 deletions mamba_ssm/ops/selective_scan_interface.py
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Original file line number Diff line number Diff line change
Expand Up @@ -300,20 +300,6 @@ def backward(ctx, dout):
delta = rearrange(delta, "b d l -> (b l) d", l=L).contiguous()
delta = rms_norm_forward(delta, ctx.dt_rms_weight, None, ctx.b_c_dt_rms_eps)
delta = rearrange(delta, "(b l) d -> b d l", l=L).contiguous()
if b_rms_weight is not None:
# Recompute & RMSNorm B
B = rearrange(B, "b 1 dstate l -> (b l) dstate", l=L).contiguous()
B = rms_norm_forward(
B, ctx.b_rms_weight, None, ctx.b_c_dt_rms_eps
)
B = rearrange(B, "(b l) dstate -> b 1 dstate l", l=L).contiguous()
if c_rms_weight is not None:
# Recompute & RMSNorm C
C = rearrange(C, "b 1 dstate l -> (b l) dstate", l=L).contiguous()
C = rms_norm_forward(
C, ctx.c_rms_weight, None, ctx.b_c_dt_rms_eps
)
C = rearrange(C, "(b l) dstate -> b 1 dstate l", l=L).contiguous()

# The kernel supports passing in a pre-allocated dz (e.g., in case we want to fuse the
# backward of selective_scan_cuda with the backward of chunk).
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