Systems and method for tracking activations to perform row hammer mitigation in memory modules
A hybrid tracker system and method are disclosed for RH mitigation, which combines the best of both SRAM and DRAM to enable low-cost mitigation of RH at ultra-low thresholds. The system consists of two structures. First, an SRAM-based structure is provided that tracks aggregated counts at the granularity of a group of rows and is sufficient for the vast majority of rows, which receive only a few activations. Second, a per-row tracker stored in the DRAM-array is provided which can track an arbitrary number of rows; however, to limit performance overheads, this tracker is used only for the small number of rows that exceed the tracking capability of the SRAM-based structure.
1 . A method for Row-hammer mitigation comprising:
determining that a row of a plurality of rows of a DRAM module has been activated, wherein the DRAM module is part of a memory device comprising the DRAM module and an SRAM module; and
in response to the determination that the row has been activated:
determining a group of rows of a plurality of groups of rows that includes the row that has been activated, wherein each group of rows includes a unique subset of rows of the plurality of rows and each row of the plurality of rows is included in a group of rows of the plurality of groups of rows;
determining that a count associated with the group of rows in a group-count table satisfies a group-count threshold, wherein the group-count table is stored in the SRAM module and not in the DRAM module, and wherein the group-count table includes a different count for each group of rows of the plurality of rows;
in response to determining that the count associated with the group of rows satisfies the group-count threshold:
incrementing a count associated with an entry for the row in a row-count table, wherein the row-count table is stored in the DRAM module and not in the SRAM module;
determining that the count associated with the entry for the row in the row-count table satisfies a row-count threshold; and
in response to the determination that the count associated with the entry for the row in the row-count table satisfies the row-count threshold, performing row hammer mitigation.
2 . The method of claim 1 , further comprising:
determining that the count associated with the group of rows in the group-count table does not satisfy the group-count threshold; and
in response to the determination that the count associated with the group of rows in the group-count table does not satisfy the group-count threshold, increment the count associated with the group of rows in the group-count table.
3 . The method of claim 1 , further comprising:
after performing the row hammer mitigation, setting the count associated with the entry for the row that has been activated to zero.
4 . The method of claim 1 , wherein the count associated with the group of rows in the group-count table satisfies the group-count threshold when the count is equal to the group-count threshold.
5 . The method of claim 1 , wherein the count associated with the entry for the row satisfies the row-count threshold when the count is equal to the row-count threshold.
6 . The method of claim 1 , wherein each row of the plurality of rows is only in one group of rows of the plurality of groups of rows.
7 . The method of claim 1 , further comprising maintaining a row-count cache of the row-count table.
8 . The method of claim 7 , wherein the row count cache is maintained in the SRAM module.
9 . The method of claim 1 , wherein the method is performed by a memory controller of the memory device.
10 . A memory device comprising:
a memory controller;
an SRAM module; and
a DRAM module comprising a plurality of rows, wherein the memory controller is adapted to:
determine that a row of the plurality of rows of the DRAM module has been activated; and
in response to the determination that the row has been activated:
determine a group of rows of a plurality of groups of rows that includes the row that has been activated, wherein each group of rows includes a unique subset of rows of the plurality of rows and each row of the plurality of rows is included in a group of rows of the plurality of groups of rows;
determine that a count associated with the group of rows in a group-count table satisfies a group-count threshold, wherein the group-count table is stored in the SRAM module and not in the DRAM module, and wherein the group-count table includes a different count for each group of rows of the plurality of rows;
in response to determining that the count associated with the group of rows satisfies the group-count threshold:
increment a count associated with an entry for the row in a row-count table, wherein the row-count table is stored in the DRAM module and not in the SRAM module;
determine that the count associated with the entry for the row in the row-count table satisfies a row-count threshold; and
in response to the determination that the count associated with the entry for the row in the row-count table satisfies the row-count threshold, perform row hammer mitigation.
11 . The memory device of claim 10 , wherein the memory device is further adapted to:
determine that the count associated with the group of rows in the group-count table does not satisfy the group-count threshold; and
in response to the determination that the count associated with the group of rows in the group-count table does not satisfy the group-count threshold, increment the count associated with the group of rows in the group-count table.
12 . The memory device of claim 10 , wherein the memory device is further adapted to:
after performing the row hammer mitigation, set the count associated with the entry for the row that has been activated to zero.
13 . The memory device of claim 10 , wherein the count associated with the group of rows in the group-count table satisfies the group-count threshold when the count is equal to the group-count threshold.
14 . The memory device of claim 10 , wherein the count associated with the entry for the row satisfies the row-count threshold when it is equal to the row-count threshold.
15 . The memory device of claim 10 , further comprising maintaining a row-count cache of the row-count table.
16 . A memory device comprising:
a memory controller;
an SRAM module; and
a DRAM module comprising a plurality of rows, wherein the memory controller is adapted to:
determine that a row of the plurality of rows of the DRAM module has been activated; and
in response to the determination that the row has been activated:
determine a group of rows of a plurality of groups of rows that includes the row that has been activated, wherein each group of rows includes a unique subset of rows of the plurality of rows and each row of the plurality of rows is included in a group of rows of the plurality of groups of rows;
determine whether a count associated with the group of rows in a group-count table is less than a group-count threshold, wherein the group-count table is stored in the SRAM module and not in the DRAM module;
if it is not determined that the count associated with the group of rows is less than the group-count threshold:
increment a count associated with an entry for the row in a row-count table, wherein the row-count table is stored in the DRAM module and not in the SRAM module;
determine that the count associated with the entry for the row in the row-count table is not less than a row-count threshold; and
in response to the determination that the count associated with the entry for the row in the row-count table is not less than the row-count threshold, perform row hammer mitigation; and
after performing the row hammer mitigation, set the count associated with the entry for the row that has been activated to zero;
if it is determined that the count associated with the group of rows is less than the group-count threshold:
increment the count associated with the group of rows in the group-count table.