The POOL_TYPE enumeration type specifies the type of system memory to allocate.

typedef enum _POOL_TYPE {
  NonPagedPool,
  PagedPool,
  NonPagedPoolMustSucceed,
  DontUseThisType,
  NonPagedPoolCacheAligned,
  PagedPoolCacheAligned,
  NonPagedPoolCacheAlignedMustS
} POOL_TYPE;

Values

NonPagedPool

Nonpaged pool, which is nonpageable system memory. Nonpaged pool can be accessed from any IRQL, but it is a scarce resource and drivers should allocate it only when necessary.

The system can allocate buffers larger than PAGE_SIZE from nonpaged pool only in multiples of PAGE_SIZE. Requests for buffers larger than PAGE_SIZE, but not a PAGE_SIZE multiple, waste nonpageable memory.

PagedPool

Paged pool, which is pageable system memory. Paged pool can only be allocated and accessed at IRQL < DISPATCH_LEVEL.

NonPagedPoolMustSucceed

This value is for internal use only, and is allowed only during system startup. Drivers must not specify this value at times other than system startup, because a "must succeed" request crashes the system if the requested memory size is unavailable.

DontUseThisType

Reserved for system use.

NonPagedPoolCacheAligned

Nonpaged pool, aligned on processor cache boundaries. This value is for internal use only.

PagedPoolCacheAligned

Paged pool, aligned on processor cache boundaries. This value is for internal use only.

NonPagedPoolCacheAlignedMustS

This value is for internal use only, and is allowed only during system startup. It is the cache-aligned equivalent of NonPagedPoolMustSucceed.

Comments

When the system allocates a buffer from pool memory of PAGE_SIZE or greater, it aligns the buffer on a page boundary. Memory requests smaller than PAGE_SIZE are not necessarily aligned on page boundaries, but these requests always fit within a single page and are aligned on an 8-byte boundary.

Requirements

Headers: Defined in Wdm.h. Include Wdm.h, Ntddk.h, or Ntifs.h.

See Also

ExAllocatePoolWithTag, ExAllocatePoolWithQuotaTag, ExAllocatePoolWithTagPriority