Methods and systems for deadlock-free allocation of memory

A system for allocating memory resources, comprising:

• a storage controller including hardware and software arranged to:
• designate I/O processes as one of updating processes and non-updating processes;
• allocate to the non-updating processes a first page reference to a first page of memory;
• allocate to the updating processes a second page reference to a second page of memory;
• copy contents of the first page to the second page;
• merge sectors of the first page to the second page after the updating processes have altered sectors of the second page;
• maintain a first reference count of the updating processes and a first shared reference count of the non-updating processes associated with the first page of memory;
• delay freeing the first page until the first shared reference count equals zero;
• increment the first shared reference count when a new non-updating process accesses the first page;
• decrement the first shared reference count when an existing non-updating process terminates;
• and
• maintain a second reference count and a second shared reference count associated with the second page, wherein the second shared reference count represents a number of non-updating processes accessing the second page and is initially set to zero.

A computer program product comprising a tangible computer-usable medium having a computer readable program embodied in the medium, wherein the computer readable program when executed on a storage controller causes the storage controller to:

• receive a first function call associated with a first process;
• designate the first process as a non-updating process;
• allocate to the first process a first page reference to a first page of memory;
• receive a second function call associated with a second process;
• designate the second process as an updating process;
• copy contents of the first page to a second page of memory;
• merge sectors of the first page to the second page after the second process has altered sectors of the second page;
• and
• delay freeing the first page until the first process terminates,
• wherein the delaying comprises:
• maintaining a first reference count and a first shared reference count associated with the first page, and
• freeing the first page when the first shared reference count equals zero,
• wherein the first shared reference count represents a number of non-updating processes accessing the first page, and
• wherein the computer readable program further causes the storage controller to:
• increment the first shared reference count when a new non-updating process accesses the first page,
• decrement the first shared reference count when an existing non-updating process terminates, and
• maintain a second reference count and a second shared reference count associated with the second page, wherein the second shared reference count represents a number of non-updating processes accessing the second page and is initially set to zero.

A method for managing memory, comprising:

• providing a direct memory access storage controller that operates to:
• designate I/O processes associated with a page of memory as one of updating and non-updating;
• allocate to the non-updating processes a first page reference to a first page of memory;
• allocate to the updating processes a second page reference to a second page of memory;
• copy contents of the first page to the second page;
• merge sectors of the first page to the second page after the updating processes have altered sectors of the second page;
• update a first reference count representing a number of updating processes associated with the first page;
• update a first shared reference count representing a total number of non-updating processes associated with the first page;
• free the page for use by other code when the first shared reference count decrements to zero;
• increment the first shared reference count when a new non-updating process accesses the first page;
• and
• decrement the first shared reference count when an existing non-updating process terminates;
• and
• maintain a second reference count and a second shared reference count associated with the second page, wherein the second shared reference count represents a number of non-updating processes accessing the second page and is initially set to zero,
• wherein the storage controller comprises a combination of hardware and software.