Change Details

Callers of swp_pager_getswapspace get either as many blocks as they requested, or none, and in the latter case it is up to them to pick a smaller request to make - which they always do by halving the failed request. This change to swp_pager_getswapspace leaves the task of downsizing the request to the function and not its caller. It still does so by halving the original request. A new parameter to blist_alloc specifies an upper bound on the size of the allocation request, so that the blocks allocated are from the next set of free blocks big enough to satisfy the minimum requirements of the request, and uses as many of those blocks as possible, up to the specified maximum. The definition of swp_pager_getswapspace uses this parameter to ask for a number of blocks between the new halved request size and the previous failed request size. Thus a request for 32 blocks may fail, but instead of getting only 16 blocks instead, the caller might get 19 or 27, which is closer to what they originally wanted. I expect this to lead to bigger block allocations and less block fragmentation, at least in some cases.

Callers of swp_pager_getswapspace get either as many blocks as they requested, or none, and in the latter case it is up to them to pick a smaller request to make - which they always do by halving the failed request. This change to swp_pager_getswapspace leaves the task of downsizing the request to the function and not its caller. It still does so by halving the original request. A new parameter to blist_alloc specifies an upper bound on the size of the allocation request, so that the blocks allocated are from the next set of free blocks big enough to satisfy the minimum requirements of the request, and the number of blocks allocated are as many as possible, up to the specified maximum. The definition of swp_pager_getswapspace uses this parameter to ask for a number of blocks between the new halved request size and the previous failed request size. Thus a request for 32 blocks may fail, but instead of getting only 16 blocks instead, the caller asks for 16 to 31 next, and might get 19 or 27, which is closer to what they originally wanted. I expect this to lead to bigger block allocations and less block fragmentation, at least in some cases.

Callers of swp_pager_getswapspace get either as many blocks as they requested, or none, and in the latter case it is up to them to pick a smaller request to make - which they always do by halving the failed request. This change to swp_pager_getswapspace leaves the task of downsizing the request to the function and not its caller. It still does so by halving the original request. A new parameter to blist_alloc specifies an upper bound on the size of the allocation request, so that the blocks allocated are from the next set of free blocks big enough to satisfy the minimum requirements of the request, and uses as manythe number of those blocksblocks allocated are as many as possible, up to the specified maximum. The definition of swp_pager_getswapspace uses this parameter to ask for a number of blocks between the new halved request size and the previous failed request size. Thus a request for 32 blocks may fail, but instead of getting only 16 blocks instead, the caller asks for 16 to 31 next, the callerand might get 19 or 27, which is closer to what they originally wanted. I expect this to lead to bigger block allocations and less block fragmentation, at least in some cases.