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man pages section 9: DDI and DKI Kernel Functions

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Updated: July 2017



btop - convert size in bytes to size in pages (round down)


#include <sys/ddi.h>

unsigned long btop(unsigned long numbytes);

Interface Level

Architecture independent level 1 (DDI/DKI).



Number of bytes.


The btop() function returns the number of memory pages that are contained in the specified number of bytes, with downward rounding in the case that the byte count is not a page multiple. For example, if the page size is 2048, then btop(4096) returns 2, and btop(4097) returns 2 as well. btop(0) returns 0.

Return Values

The return value is always the number of pages. There are no invalid input values, and therefore no error return values.


The btop() function can be called from user, interrupt, or kernel context.

See Also

btopr(9F), ddi_btop(9F), ptob(9F)

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